Small Cell Prostate Cancer Clinical Trials

(frequently updated)

Small Cell Prostate Cancer (SCPC), and more generally Neuroendocrine Prostate Cancer (NEPC), are thankfully rare types of prostate cancers. They are not responsive to hormone therapy, to taxanes (Taxotere or Jevtana), or to radiation. They are difficult to detect and monitor with the kinds of imaging used to detect prostate adenocarcinoma (mpMRI, bone scans, PSMA PET scans), but may show up with FDG PET (see this link). They do not put out PSA, PAP or bone alkaline phosphatase. Special biochemical tests or biopsies for chromogranin A, neuron-specific enolase (NSE), synaptophysin,  DLL-3, CD56, and other biomarkers are required. It often appears at a "mixed type." 

Sub-types

Not all neuroendocrine prostate cancers carry the same prognosis. Aggarwal identified a sub-type that became prevalent in 17% of patients who were heavily pretreated with enzalutamide (Xtandi) and abiraterone (Zytiga). He calls this "treatment-emergent small cell neuroendocrine prostate cancer (t-SCNC). The pre-treatment probably selected for this subtype that may be partially responsive to familiar therapies. The "treatment-emergent" subtype and the small amounts sometimes detected initial biopsies do not appear to be as virulent (see this link). There are some studies that indicate that they may appear spontaneously in later stages of normal prostate cancer development. Aggarwal commented:

“Although long term androgen deprivation therapy may be associated with the development of treatment-emergent small cell neuroendocrine prostate cancer (t-SCNC) in a minority of patients, multiple studies have confirmed the long-term benefit of abiraterone and enzalutamide for prostate cancer patients in various disease settings. Use of these agents should not be limited by concern for the subsequent development of t-SCNC.”

Aggarwal has announced a clinical trial where he will be testing a combination of Xtandi, Keytruda, and ZEN-3694 in (among others) a group of men identified with the t-SCNC subtype. ZEN-3694 is an experimental medicine that inhibits a gene called MYC, which is often over-expressed in advanced prostate cancer. 

Aggarwal is also testing FOR-46 targeting the CD-46 protein that often is expressed in neuroendocrine tumors.

177Lu Basket Trial (begins June 18, 2024)

Because there are several subtypes of neuroendocrine PCa, Novartis is running a trial that takes patients with 3 different subtypes and treats them with a radiopharmaceutical with the most appropriate ligand tailored to the dominant subtype. A biopsy determines whether it is neuroendocrine and which of 3 subtypes predominates. 177Lu is attached to any of the following 3 ligands:

1. PSMA
2. SSTR2 (Somatostatin receptor)
3. GRPR (Gonadotropin releasing hormone receptor)

Chemotherapy

Because of the "mixed type," chemo often includes a taxane. More often, a platin is mixed in a cocktail with another chemo agent, like etoposide. A couple of case reports from Japan (see this link and this one) reported some success with a platin combined with irinotecan.

This clinical trial at Duke has two chemotherapies (cabazitaxel and carboplatin), as well as two checkpoint blockade-type immunotherapies (nivolumab and ipilimumab):

CHAMP

Nuclear Medicine/ Somatostatin

The Urology Cancer Center in Omaha, Nebraska has announced a clinical trial of 225Ac-FPI-2059 for neuroendocrine cancers. FPI-2059 is a small molecule that attaches to the neurotensin receptor 1 peptide that is expressed by neuroendocrine cancer cells.

Another radiopharmaceutical has been tried by the nuclear medicine department at the University of Heidelberg. I suggest that anyone who is interested email or call (they all speak English) Uwe_Haberkorn@med.uni-heidelberg.de Phone: 06221/56 7731. With the euro now at close to parity with the dollar, this medical tourism is an especially attractive option:

213Bi-DOTATOC shows efficacy in targeting neuroendocrine tumors

A similar radiopharmaceutical using Lu-177-DOTATATE (called Lutathera) has been FDA-approved for small cell cancer affecting the digestive tract. DOTATOC (and also DOTATEC and DOTATATE) binds to somatostatin receptors on the small cell digestive tract cancer surface, where it is highly expressed. It is rarely expressed in small-cell prostate cancer, but there have been some isolated case reports like this one or small trials like this one. This means that treatment with a somatostatin analog (octreotide, lanreotide, or pasireotide) may be somewhat effective even without the radioactive emitter attached to it. These drugs are available now in the US, are not toxic, and your doctor can prescribe them without a clinical trial. there is a clinical trial of it in London for any solid tumor:

https://clinicaltrials.gov/ct2/show/NCT02236910

These clinical trials include somatostatins:

https://clinicaltrials.gov/ct2/show/NCT01794793
https://clinicaltrials.gov/ct2/show/NCT02754297

This clinical trial at Johns Hopkins uses Lutathera to treat neuroendocrine prostate cancer, specifically:

https://clinicaltrials.gov/ct2/show/NCT05691465

While the presence of somatostatin receptors in the tumor can be determined by pathological analysis (immunohistochemical (IHC) staining for SSTR2), there is an FDA-approved PET scan that uses Ga-68-DOTATATE that can detect it without a biopsy. It is used to detect neuroendocrine tumors that are often non-prostatic. Researchers at Emory found that Ga-68-DOTATATE uptake is higher even in neuroendocrine tumors of prostatic origin, which suggests that somatostatin-based therapy may be beneficial. (One patient who was positive for a BRCA2 mutation but negative for NEPC had high uptake as well.)

DLL3

DLL3 is a protein that is expressed on the surface of neuroendocrine cells regardless of the cancer of origin, and has been identified in two-thirds of neuroendocrine prostate cancer (NEPC) cells. An antibody linked to a chemotherapy, called Rova-T, against DLL3 has been developed and has shown some promise against NEPC in a preclinical study. Unfortunately, AbbVie discontinued R&D after it failed to meet goals for small cell lung cancer (SCLC). A Phase 2 trial that included NEPC was discontinued. Misha Beltran at Dana Farber has tried an antibody-drug conjugate (rovalpituzumab teserine) targeted to DLL3 on a single patient. After two treatments, his metastases shrank and stabilized.

Harpoon has announced a clinical trial of HPN328  for people with advanced cancers that express DLL3. HPN328 is a bispecific T-cell engager (BiTE) that targets DLL3 and also promotes T cells to attack those cells exhibiting it. AMG757 is also a BiTE. Amgen has announced a clinical trial of AMG 757 for advanced prostate cancer. Phanes Therapeutics has a BiTE clinical trial targeting DLL3.

AMG119 is a CAR-T therapy that targets DLL-3. CAR-T involves treating one's own T-cells by sensitizing them to DLL3. Both of these create a T-cell and a cytokine response in environments that otherwise have low immune cell activity. That response may kill bystander cells, and through a phenomenon called "antigen spreading," may be able to kill other cancer cells that do not exhibit DLL3. (BiTE and CAR-T therapies that target PSMA are  in clinical trials noted at end of this article)

The Wang Lab at Duke has specific expertise in morphological analysis of NEPC and IHC staining for DLL3. It may be a good idea to get a second opinion from them.

Checkpoint blockade

Another recent discovery is that PD-L1 is highly expressed in SCPC. This opens the door to immunotherapies that target the PD-1/PD-L1 pathway, like Keytruda.

PD-L1 expression in small cell neuroendocrine carcinomas

Small clinical trials have so far shown little benefit:

Avelumab (Duke)

Pembrolizumab (UCLA)

Why Lutetium-177-PSMA treatment sometimes may not help, and may even harm

(updated)

Lu-177-PSMA usually improves survival

We've seen in a couple of small trials in Germany and Australia that Lu-177-PSMA seemed to provide better than expected survival. In Germany, median overall survival was 12.9 months across 104 patients. In Australia, median overall survival was 13.3 months across 50 treated patients. In both trials, all or almost all patients had already received taxane chemotherapy and either enzalutamide or abiraterone. There was no control group in either trial, so we can only guess at what overall survival would have been without the therapy.

In the "ALSYMPCA" trial of Xofigo, among the subgroup of patients who had received docetaxel for their painful mCRPC (see this link),  median overall survival was 14.4 months with Xofigo vs. 11.3 months with placebo. The ALSYMPCA trial was conducted before abiraterone and enzalutamide were approved, so it is impossible to know how prior treatment with one of those might have changed survival.

In a recent trial of Jevtana as a third-line therapy, after docetaxel and either abiraterone or enzalutamide, median overall survival was 13.6 months for Jevtana vs. 11.6 months for the other second-line hormonal. 

So, in heavily pre-treated patients, Lu-177-PSMA seems to improve survival about as well as Xofigo or Jevtana when used as a third-line therapy. The VISION trial  found that LuPSMA treatment increases survival by 5 months in heavily treated patients (similar to Xofigo).

PSA is not always a good indicator of effectiveness, as has been found for Xofigo and Provenge. Lu-177-PSMA reduced PSA in about 2/3 of treated patients in most studies. That leaves about 1/3 of patients who derived no benefit (even though they had PSMA-avid tumors), and waterfall plots showed that a few patients had large increases in PSA following PSMA-targeted therapy.

It is worth noting that the PSMA protein contributes to the survival of the cancer, and just the PSMA ligand that attaches to it has some activity in delaying progression, even without a radioactive component (similar to the way an anti-androgen attaches to the androgen receptor, delaying progression). It is also worth noting that ADT initially increases PSMA expression, but decreases its expression with continued use.

The opportunities are:

• to select patients who are likely to benefit
• give alternative therapies (like Jevtana) to patients who are unlikely to benefit
• provide adjuvant therapies that may increase survival

PSMA avidity - optimal point in time

It has long been known that PSMA is a moving target. The advent of PSMA PET scans has enabled us to track PSMA expression. Cancers that express a lot of PSMA (called PSMA-avid tumors) can be distinguished from cancers that express very little. Radiologists determine avidity by comparing the uptake of the tracer in cells that express PSMA to the uptake of the tracer in cells known to not express PSMA. Early low-grade prostate cancer does not express PSMA at all. Higher grade prostate cancer may express some PSMA. PSMA expression really starts to take off when the cancer metastasizes, although it is highly variable between patients. About 90-95% of metastatic men express at least some PSMA on their prostate cancer cells. At some point, however, as genomic breakdown continues, PSMA is no longer expressed by metastases. Treating when PSMA is not adequately expressed can cause a lot of toxicity to healthy tissues (especially kidneys and salivary glands) and little therapy (see this link and this one). Thus, there is an optimal point for treating each patient with PSMA-targeted therapy. Treatment too early or too late, may exert selective pressure on the predominant non-PSMA-types, allowing them to take over.

Michael Hofman and others at the Peter MacCallum Cancer Center in Melbourne (see this presentation and this link) have initiated several clinical trials using Lu-177-PSMA at earlier stages of disease progression:

• #lutectomy trial (Declan Murphy,  PI) is treating PSMA-avid high-risk patients with Lu-177-PSMA, followed by prostatectomy and pelvic lymph node dissection
• #upfrontPSMA (Arun Asad, PI) is treating patients first diagnosed with high volume metastases with Lu-177-PSMA + ADT + docetaxel vs ADT + docetaxel.

Other opportunities for early use include Lu-177-PSMA treatment for those in the following settings:

• active surveillance
• persistent PSA after prostatectomy
• salvage treatment after first recurrence
• salvage treatment after second recurrence
• metastatic CRPC before docetaxel or advanced hormonal therapies
• non-metastastic (on bone scan/CT) CRPC before docetaxel or advanced hormonal therapies

Centers in Germany may be willing to treat patients per protocol (i.e., outside of a clinical trial) in some of those situations.

Repopulation

In radiobiology, one of the ways in which radiation can fail to destroy cancer is called repopulation. It means that when radiation kills some cancer cells but leaves many behind, the remaining ones now have access to space in which to expand and access to nutrients and oxygen that the other cancer cells had deprived them of. Paradoxically, the tumor can then grow faster than it ever would have before the treatment. This is sometimes seen with rapidly growing tumors, as some head and neck cancers. They sometimes irradiate those cancers multiple times a day to prevent repopulation.

Repopulation is never seen with X-ray (or proton) treatment of relatively slow-growing prostate cancers. X-rays penetrate throughout the prostate and kill all the cancer there. If there is any survival of an oxygen-deprived tumor core, it will be killed by the next fraction of X-rays in a day or two. However, Lu-177 emits beta rays that may only penetrate to about 125 cells around each target. Ac-225 (also sometimes used in PSMA therapy) only kills about 8 cells around each target. With such short-range killing, there is a real danger of repopulation if there are insufficient PSMA targets within the tumor. Multiple treatments are usually not given for several weeks, and the tumors may have changed by then.

PSMA heterogeneity

What we have learned recently is that not only does PSMA expression change over time, but in a given patient, some tumors may express PSMA and some may not. Moreover, even within a single tumor, some cells may express PSMA and some may not.

Paschalis et al. looked at the degree of PSMA expression of 60 patients with metastatic castration-resistant prostate cancer (mCRPC). They also looked at tissue samples of 38 of them taken when they were diagnosed with hormone-sensitive prostate cancer (HSPC). To detect the amount of PSMA expressed, they used an antibody stain that attaches to the part of the PSMA protein that lies above the cellular membrane. They rated the tumors "0" if there was no PSMA up to "300" if all cells expressed PSMA. They also performed a genomic analysis, looking for mutations in over 100 genes associated with DNA-repair defects.

Among the tumor samples from men with HSPC they found:

• 42% of the 38 men with HSPC  had no PSMA at diagnosis - it only emerged later
• 5 of the 6 HSPC men diagnosed with Gleason score 6 or 7 had little or no PSMA expression at that time
• About half of 30 HSPC men diagnosed with Gleason score 8-10 had little or no PSMA expression at that time
• Those who expressed PSMA had a worse prognosis
• Expression of PSMA varied greatly (heterogeneous) between patients
• Expression of PSMA varied greatly between biopsy samples from the same patient
• The higher the PSMA expression in a patient, the greater the amount of PSMA heterogeneity

Among the tumor samples from the 60 men with mCRPC they found:

• PSMA expression had increased from when they were diagnosed with HSPC
• Half of the tumors with no PSMA at HSPC diagnosis continued to have no PSMA
• 73% expressed PSMA; 27% did not - only 1 of whom had neuroendocrine prostate cancer
• 84% of those expressing PSMA exhibited marked PSMA heterogeneity
• Heterogeneous patterns were identified:

• PSMA positive and negative cells interspersed in a single area
• PSMA-positive islands in a sea of PSMA-negative cells
• PSMA-positive regions separated by >2 mm from PSMA-negative regions
• Some metastases wholly PSMA-positive, some wholly PSMA-negative in the same patient

• Bone and lymph node metastases had similar PSMA expression; liver metastases (none neuroendocrine) had lower PSMA expression

Analysis of DNA-repair defects revealed:

• mCRPC patients with DNA-repair defects had higher PSMA expression
• HSPC patients without DNA-repair defects were less likely to become PSMA-positive
• Patients treated with PARP inhibitors were more likely to respond if they were PSMA-positive
• For validation, in a separate sample of tumors, those with DNA-repair defects were found to have much higher PSMA expression than those without such defects. This was especially true for somatic mutations in BRCA2, ATM, and dMMR.
• PSMA was downregulated in androgen-independent basal cancer cells (resistant to advanced anti-androgens) and neuroendocrine cells.

The significance of this study is that it may explain why about a third of PSMA-avid patients do not respond to Lu-177-PSMA therapy. The emitted beta particles may kill cells within about 125 cells from where they are attached at the PSMA site. Thus cells that do not express PSMA that are more than 2 mm from a PSMA-avid site will not be killed (see "Repopulation" above).

The authors hypothesize that DNA-damage repair defects cause PSMA to proliferate. If they are right, a PARP inhibitor (like olaparib), which has also been found to be effective when there are DNA-repair defects (see this link), may be able to increase the efficacy of PSMA treatment. This is the subject of an ongoing clinical trial.

(update 2/24/23) Sayar et al. report the results of a PSMA autopsy study.

• 25% had no detectable PSMA
• 44% had heterogeneous PSMA expression in multiple metastases
• 63% had at least one PSMA-negative metastasis
• Loss of PSMA expression was linked to epigenetic changes on the FOLH1 gene
• Treatment of cells (in vivo and in vitro) with HDAC inhibitors restored PSMA expression
  

HDAC inhibitors are available off-label and include: Valproic Acid (Depakote), Zolinza (vorinostat), Beleotaq (belinostat), Faridak (panobinostat), and Buphenyl (phenylbutyrate).

Practical detection of heterogeneity/ clinical trials

Now that we know that heterogeneity can impact Lu-177-PSMA effectiveness, it behooves us to find a way of determining the degree of heterogeneity without doing a biopsy of every single metastatic site. One way is to give each patient two PET scans, so they could see the sites that exhibited PSMA expression as well as the sites that exhibited high uptake on an FDG PET scan.

It is futile to offer PSMA-targeted therapy if there are many sites that show up only on an FDG PET scan but few sites that display uptake of PSMA. It also may be futile to treat patients that show some sites where PSMA and FDG sites do not overlap - "discordant." On the other hand, where there is a high degree of overlap between FDG and PSMA - "concordant" - the PSMA radiotherapy will kill both cancers simultaneously. Of course, the ideal candidate would display only highly PSMA-avid sites.  Thang et al. reported on the survival of 30 patients who were treated with Lu-177-PSMA (who were either high PSMA/low FDG or concordant, compared to 16 patients who were excluded based on lack of PSMA (8 patients) or a high degree of discordant sites (8 patients). All patients were heavily pretreated.

• Treated patients survived 13.3 months (median)
• Untreated patients survived 2.5 months (median)

(update 12/2020) Michalski et al. looked at 54 patients. Some had at least one tumor that was positive on FDG, but negative on PSMA (FDG+/ PSMA-). They compared outcomes to patients that had only PSMA+ tumors. They found:

• A third of patients had at least one FDG+/PSMA- tumor
• Overall survival was FDG+/PSMA- patients was 6 months
• Overall survival for PSMA+only patients was 16 months

(update 2/16/22) A secondary analysis of the TheraP trial of Jevtana vs LuPSMA looked at patient response depending on whether their cancer showed up also on FDG PET scans. They looked at the percent of men whose PSA reduced by 50% or more (PSA50) in the cohort that received cabazitaxel vs the cohort that received Lu177PSMA. Each cohort was analyzed according to whether they were highly avid on a PSMA PET scan (SUVmean≥10) "high PSMA" and whether their metabolic tumor volume on an FDG scan was greater than 200ml (MTV≥200) "high FDG". They required high PSMA (SUVmax≥20), and excluded men who were FDG+ and PSMA-.

• In men with high PSMA, the PSA50 was 91% for Lu177PSMA vs 47% for cabazitaxel
• Among men with high PSMA, the odds ratio of responding to Lu177PSMA was 12.2 vs 2.2 for cabazitaxel 
• In men with low PSMA, the PSA50 was 52% for Lu177PSMA vs 32% for cabazitaxel
• In men with high FDG, the PSA50 was 57% for Lu177PSMA vs 20% for cabazitaxel
• Among men with a high FDG, the odds ratio of any response to either treatment was 0.44
• In men with low FDG, the PSA50 was 70% for Lu177PSMA vs 44% for cabazitaxel

It is unknown whether the survival of untreated patients might be longer or shorter had they received treatment. It is possible that discordant patients may benefit from sequenced (before or after) or concomitant treatment with:

• chemotherapy- 
• for non-discordant, newly diagnosed, with high-volume metastases in Australia
• for patients who have progressed after an advanced hormonal and docetaxel, this Australian trial combines it with cabazitaxel.
• immunotherapy: 
•  trials of adjuvant Keytruda in UCSF and Melbourne
•  trial of combo with Keytruda and Yervoy in Australia
•  trials of a bispecific PSMA/ T cell-recruiting antibody (BiTE) in: 
1. Los Angeles, Europe & Australia (AMG 160) (early results)
2. AMG 160 + Xtandi/Zytiga + PD1i
3. City of Hope, LA AMG 509
4.  NY (REGN5678) -> trial ended for toxicity
5. Germany AMG 212 (CD3/CC1) (Phase 1 results)
6. various US sites (HPN 424) (early results) -> trial ended
7.  various sites in N. America (JNJ 63898081)
8. TNB-585 (5 US sites)
9. CB-307 (UK)
10. LAVA1207 (4 US sites)
11. JNJ-80038114 (Nashville, France, Germany, UK)
• trial of a CAR-T/PSMA therapy at UOP, Thomas Jefferson U & Columbia and Shanghai and City of Hope
• Phase 2 trial (completed) of Progenics' antibody-drug conjugate  (PSMA ADC 2301)
• Xofigo for bone metastases - trial of a therapy that may include both
• With EBRT to oligomets in recurrent patients in Australia
• PARP inhibition - trial in Melbourne
• Enzalutamide (Xtandi) randomized trial in Australia
• Adding a systemic radiosensitizer: Veyonda (idronoxil) suppository. A phase I/II trial  found it was safe, with only anal inflammation attributable to the suppository. Results were no better than trials without the radiosensitizer; however, unlike those other trials, almost all (91%) patients had already received Jevtana.
• other novel non-PSMA targeted treatments

It is possible that such adjuvant treatment may decrease the population of discordant sites, and minimize repopulation effects.

Based on this new knowledge, it is recommended that patients who are good candidates for Lu-177-PSMA therapy have both a PSMA PET/CT scan and an FDG PET/CT at around the same time. FDG PET scans are generally covered by insurance; PSMA PET scans are not covered by insurance yet.

The Perils and Pitfalls of "Treating PSA" in Advanced Prostate Cancer

Prostate Specific Antigen (PSA) is a protein on the surface of all benign prostate cells and most malignant prostate cancer cells. In prostate cancer, expression of PSA is correlated with the size of the tumor (see this link). When prostate cancer first metastasizes, the tumor is limited in size by its blood supply. As it grows, the cancer creates its own blood supply by secreting growth factors called VEGF. The PSA from the cancer activates VEGF to form blood vessels that bring oxygen and nutrients to the cancer and lymph vessels to drain fluids from the growing tumor (see this link). Tumor blood supplies are not as patent as those of benign tissues. Healthy prostate tissues with patent blood supply, and micrometastases that have little or no blood supply put out very little detectable PSA into the serum (although the cells express high levels of PSA). But the leaky blood supply of tumors allows PSA to enter the serum where it is detected by a PSA test. So, the larger, more established tumors of a given patient create almost all of his detectable PSA (see this link).

"Treating PSA"

I. Selecting for low PSA subtypes

For most men with advanced prostate cancer, PSA is their best biomarker of progression - more detected PSA means more progression. This may change as the cancer evolves. A highly mutated tumor may put out less PSA. Highly undifferentiated kinds of prostate cancer, and other relatively rare sub-types (e.g., ductal, neuroendocrine, basal cell, "double negative," etc.) may evince little or no serum PSA.  

So it is possible, when such phenotypes are present and they are mixed with "normal" prostate cancer, to provide treatments that kill off the "normal" prostate cancer cells, leaving the low-PSA subtypes behind. Such a situation has been identified in patients heavily treated with chemo and enzalutamide. It is called "treatment-emergent neuroendocrine prostate cancer" (see this link) and has been identified in 17% of heavily-treated patients. 

Another example of a treatment that may select for low-PSA subtypes is Lu-177-PSMA. If the patient has two types of prostate cancer, one that expresses PSMA and PSA, while his other cancer expresses neither, PSMA-targeted therapy may eliminate the source of most of the PSA, leaving more virulent subtypes behind (see this link). 

This type of situation is dangerous if one relies on PSA as the principal biomarker of progression. One may be lulled into complacency by deceptively low PSA.

It is worth noting that two FDA-approved therapies for prostate cancer, Provenge and Xofigo,  have been proven to increase survival, but have little or no effect on PSA.

II. Supplements that interfere with PSA tests

Patients often self-medicate in the hope of wresting some control over their cancer. The internet is full of "evidence" that this or that natural supplement may slow progression or even cure the cancer.  Serum PSA is detected by an antibody that can detect amounts as low as a nanogram of PSA per ml of serum. This kind of sensitivity has a cost - the antibodies are subject to interference by other substances that may be present in the serum. So far, the list of substances that may interfere with PSA tests, creating false negatives, includes biotin, curcumin, genistein, EGCG, resveratrol, capsaicin, saw palmetto, pygeum, beta-sitosterol, and statins (see this link). The false negative PSA readings may fool the patient and his physician (who may not be aware of the patient's supplement use) into believing that the cancer is under more control than it really is. Patients who use any complementary therapies are twice as likely to die of their cancer (see this link).

III. SBRT of oligometastases

1. Exponential growth

Because of Covid-19, many of us are now used to seeing exponential growth curves. Deaths from Covid-19 started very slowly in December through February. But then in March, the number of deaths climbed markedly. This illustrates the two striking features of exponential growth - the "flat" part with a very slow increase, followed by a "steep" part with a very rapid increase.

Among the biological systems that also follow an exponential growth curve are bacteria, viruses, and cancers. Here is a prototypical graph of the number of metastases in a patient.

In men who are PSA-recurrent after prostatectomy, it takes a median of 8 years for the first metastasis to become detectable (see this link). After that, I've seen that more than a year can go by between the detection of the first metastasis and the next one. Some researchers, who should know better, observed that in their patients who had early metastases treated with radiation, new metastases did not occur for a long time. They attributed the delay to the treatment rather than the natural history of metastatic progression  (see this link). It is impossible to know if there was a delay in progression without a randomized clinical trial.

What is really happening during this extended time period? The accepted theory is called "seed and soil." There are millions of cancer "seeds" in the serum, the lymph, around nerves, and hiding in various tissue reservoirs (mainly in bone tissue). While they appear to be quiescent, they are in fact changing the "microenvironment" of the tissue they are in. They are transforming the tissue to make it more conducive to prostate cancer growth, building networks of collagen, fat, blood vessels and nerves, influencing healthy cells to become cancerous, and preventing the immune system from destroying the new nests (see this link for a fuller explanation).

Because it takes such a long time to build up the metastases to the point that they are detectable by even our most sensitive PET/CT scan (the tumor detection limit is about 4 mm - millions of cells), it seems that there is little there and even less going on. This is called "oligometastatic" cancer. It seems like all the cancer can be picked off by playing whack-a-mole -- zapping the few detected metastases with intense radiation (called SBRT) as they are detected. In fact, it is well-established that SBRT provides excellent "local control." "Local control" means that the metastases are usually completely annihilated by just one or two "zaps" (see this link). Because the detected metastases are the source of almost all the PSA, PSA can fall to undetectable levels after such treatment of oligometastases. But the cancer is far from cured - the PSA has been treated, but the cancer is still micrometastatic and systemic.

Those who believe that such treatment can result in a durable remission believe that the immune system can clean up the rest of the cancer.  The ORIOLE trial (reviewed here) showed that SBRT created a T-cell response. If that T-cell response is sustained, they argue, the activated immune system can "clean up" the rest of the cancer. The skeptics argue that T-cell responses are usually not sustained. Trials of numerous immunotherapies (e.g., Prostvac, GVAX, GM-CSF, etc.) have failed to show a benefit because the early T-cell responses are countered by adaptive responses. Prostate cancer is notoriously "cold" to immunotherapies.

2. PSA-based Endpoints

What we really want to know is this: will the treatment enable patients to live longer? Overall survival is the gold standard of success of randomized clinical trials. The "problem" for clinical trials is that prostate cancer is such a slow killer, that it may take 15 years or more to discern a difference (see this link) if patients have localized or recurrent prostate cancer at the start. (For most other types of cancer, 5-year overall survival is more than adequate.) Clinical trials are often ended when half of the control group die (median survival). But, depending on patient characteristics at the start, median survival may never be reached within the duration of the clinical trial (see this link and this one and this one).

Prostate cancer-specific survival (how long before patients succumbed to their prostate cancer) is little better. It is also hampered by the fact that patients with prostate cancer may die of something else sooner, possibly because their cancer was debilitating. It is often unclear to the doctor who signs the death certificate whether the cancer was the end cause, a contributing cause, or a non-contributing factor. To get clinical trial results before new medical science and technology renders the results irrelevant, we want to use surrogate endpoints that are highly correlated with and predict overall survival.

The earliest endpoints that can be used to measure the success of a prostate cancer therapy are PSA based. All of the following surrogate/secondary endpoints are PSA based:

• PSA50 - the percent who had a reduction in PSA by 50% or more
• Nadir PSA - the lowest PSA reached after therapy (see this link)
• PSA doubling time (PSADT) - whether the therapy slowed PSA growth
• Biochemical recurrence (BCR) - depending on initial treatment, and there may be multiple salvage therapies, each with a PSA failure defined for it (see this link)
• Biochemical Recurrence-Free Survival (bRFS)
• Biochemical Disease-Free Survival (bDFS)
• Biochemical failure (BF)- rise in PSA by a pre-specified amount post-therapy
• Biochemical No Evidence of Disease (bNED)
• Time to BCR/ BF
• Time to start of lifelong ADT (based primarily on a pre-defined PSA failure benchmark)
• Failure-free survival (FFS) or Progression-free survival (PFS) or Event-free survival (EFS) - defined as BF or radiological progression or clinical progression or death. 

The following surrogate endpoints are not PSA-based:

• Clinical Progression-Free Survival (cPFS) - worsening of symptoms or performance status (see this link)
• Radiographic Progression-free Survival (rPFS) or Disease-free survival (DFS)- progression on scans or death
• Objective Response Rate (ORR) - tumor size or number reduction using RECIST criteria
• Change in Bone Scan Index
• Time to radiographic progression or failure
• Metastasis-free survival (MFS)
• Clinical progression - pain, bone fracture, spinal compression

As an example of circular reasoning, we can see in the ORIOLE trial that 6-month Progression Free Survival (PFS) was chosen as the primary endpoint. PFS was defined as  PSA progression (by >25% over nadir and by > 2 ng/ml) or radiographic progression or death. As we can readily see in the exponential growth curve, the odds of a new metastasis on a bone scan/CT are very low and there are not likely to be any deaths. Therefore, PFS was almost entirely PSA progression. But the protocol "treated PSA." It is therefore illogical to conclude, even for a Phase II trial, that oligometastatic treatment slowed progression.

(Update 8/25/2022) Deek et al. combined ORIOLE and STOMP (n=162) with extended follow-up. After 52.5 months of median follow-up, they report:

• Progression-free survival (PFS) was 11.9 mo. for metastasis-directed therapy (MDT) vs. 5.9 mos. for observation. (HR=0.44)
• Radiographic progression-free survival (rPFS) was not significantly different
• Time to castration resistance was not significantly different
• Overall survival was not significantly different
• PFS increased by about 5-6 months regardless of whether there were high-risk mutations (BRCA, ATM, RB1, TP53).
• rPFS did not significantly increase for either group.

What is confusing is the endpoint used in this analysis. 

Progression-free survival (PFS) = 

1. a PSA rise, or 
2. radiographic progression, or 
3. new symptoms, or 
4. initiation of ADT, or 
5. death.

In 52.5 months, there was very low mortality (5), and asymptomatic local control is good (3). Initiation of ADT (4) is always based on either rise in PSA (1) or radiographic progression (2). So with no difference in rPFS, the difference between PFS and rPFS is just PSA. This suggests that the extended follow-up found that MDT only treated PSA without any real impact on survival or progression of the cancer.

(Update 10/26/2022) Another example of circular reasoning can be seen in the EXTEND trial from MD Anderson. They randomized oligometastatic patients to receive metastasis-directed therapy (MDT) + ADT or ADT alone. They only evaluated "progression-free survival" which, at 22 months, was almost entirely lack of PSA progression. They claimed that the lack of PSA progression made it safe to give patients a break from ADT.

It is worth noting that radiation of the prostate ("debulking") has no survival or progression advantage when there are multiple metastases, only when the metastatic burden is low (see this link). The prostate is, of course, the source of all metastases, and an ideal environment for metastases to develop and grow. Metastasis-to-prostate spread has been observed. In a meta-analysis of the two debulking trials called STOPCAP M1, researchers found that there was a statistically significant reduction in PSA progression (by 26%), even when there was no benefit in terms of metastatic progression or survival. Treating PSA even by debulking the entire prostate is not in and of itself of any oncological benefit (there may be a palliative benefit, however).

3. Danger of Withholding Early ADT

While ORIOLE, STOMP, and SABR-COMET were Phase 2 clinical trials whose results were not meant to change practice, many patients and their doctors (often under pressure from patients) would like to believe they do. If the metastases are in places that are safe to irradiate (e.g., away from the mediastinum), there is little risk in doing so. However, if they do not understand the circular reasoning evident in the ORIOLE trial, they may put off therapies that are known to increase survival. There is also a risk of unreasonable expectations.

Some patients (and doctors) believe that by delaying ADT, they can increase their quality of life, and delay castration resistance. Neither is true. Contrary to popular belief, decreasing the intensity of hormone therapy and delaying its use brings earlier castration resistance and death. The strongest evidence for this comes from the STAMPEDE (on Zytiga and Xtandi), LATITUDE, and SPARTAN trials. Among men who were newly diagnosed with metastatic prostate cancer:

• Overall survival was longer if men used Zytiga + ADT.
• No difference based on the number of metastases
• Failure-free survival was longer if they used Zytiga  + ADT
• Overall survival was longer if men used Xtandi+ADT
• Survival was especially lengthened if there were fewer metastases 
• PSA progression-free survival was longer if they used Xtandi+ADT
• Overall survival was longer if men used Erleada+ADT
• PSA progression-free survival was longer if they used Erleada+ADT

A clear pattern emerges: early use of intensive hormone therapy prolongs survival and prolongs the time to castration resistance. Men who were oligometastatic benefited from early, intense hormone therapy.

The TROG 03.04 RADAR trial examined the duration of hormone therapy in high-risk men treated with radiation.  They found that, after 10 years of follow-up, men treated with 18 months of ADT survived longer, and reached castration resistance later compared to men treated with 6 months of ADT.

The TOAD trial looked at starting ADT at the first sign of recurrence vs. waiting for metastases to be detected. Men treated earlier reached castration resistance later. It also showed there was no major detriment to global health-related quality of life by starting ADT earlier (see this link).

Maha Hussain reported the results of a randomized clinical trial comparing intermittent vs continuous ADT in recurrent men with metastases. She found that:

• Time to castration resistance was not different for the two protocols (Figure S5)
• For men with minimal disease, overall survival was 6.9 years for those on continuous therapy vs 5.4 years for those on intermittent therapy. The trial was underpowered for this difference to reach statistical significance.
• It took 4-5 years for the survival curves to start separating - long follow-up is needed to detect survival differences.

Taken together, all these major randomized clinical trials show that the best way to use ADT in the oligometastatic setting is to use it early and heavily. Reducing the number of cancer cells as quickly and effectively as possible, even reducing those cells that haven't begun to measurably contribute to PSA, extends survival. The effect of evolutionary selection pressure allowing castration-resistant cells to survive is dwarfed by the reduction in sheer numbers. Circular reasoning may harm patients.

4. Future Clinical trials

We have learned some lessons about clinical trials for oligometastatic treatment:

• It has to have long enough follow-up, depending on the setting: at least 5 years for  newly diagnosed or recurrent men to allow time to get to the steep part of the exponential curve. It will take longer if more sensitive imaging is used.
• It must use radiographic progression-free survival, or similar, as its primary endpoint
• It must not use a PSA-related endpoint
• ADT must be used in at least the control group. It would be unethical to withhold the standard of care (see AUA Guidelines for Advanced Prostate Cancer (mHSPC 14-18)) .
• It should preferably use a PSMA PET/CT to locate metastases. The ORIOLE trial only found an advantage if patients were oligometastatic on both a PSMA PET/CT and a bone scan/CT. The use of more sensitive imaging will move the starting point to the left on the exponential curve, so it will take that much longer to detect a benefit.

These randomized clinical trials (RCTs) are currently active:

• The CORE RCT at Royal Marsden Hospital in London will have 5 years of follow-up (completion in Oct. 2024) and will include freedom from widespread metastatic disease and overall survival among the outcomes looked at. 
• The PCX IX RCT (among castration-resistant patients) at Jewish General Hospital in Montreal will have 5 years of follow-up (primary outcome in April 2025) and has radiographic progression-free survival as its primary outcome. 
• The PLATON RCT (among hormone-sensitive patients) in Canada will have 6 years of follow-up (primary outcome in July 2025) and has radiographic progression-free survival as its secondary outcome. Oligometastatic men who have never had their prostates treated with RT will have prostate radiation too in both arms. ADT is given in both arms, advanced hormonals and chemo at the physician's discretion.
• The STEREO-OS RCT (study completion in Jan 2026) in France will look at radiographic progression-free survival with follow-up of up to 3 years. 
• The FORCE RCT at the University of Michigan (only recruited 13, primary completion in 2023) will compare systemic treatment with ADT and any of Taxotere, Zytiga or Xtandi (at the discretion of the treating physician) to similar systemic treatment plus metastasis-directed SBRT for men with mCRPC who have not yet had any of those advanced systemic therapies. They will evaluate progression-free survival after 18 months. "Progression" is defined as alive and at least a 20% increase (and at least 5 mm net increase) in the size of tumors or any new metastases. They will detect metastases via bone scan/CT, However, they will also test whether PSMA-based PET indicators are as useful among men with mCRPC as it is in men with newly recurrent disease.
• The VA STARPORT RCT (primary completion in 2025) in many VA hospitals in the US will randomize patients to systemic therapy + PET-directed radiation to 1-5 oligorecurrences or to systemic therapy alone. Unfortunately, they are using castration-resistance as their primary endpoint, which is problematic.
• The START-MET RCT (primary completion in 2025) in Spain will randomize recurrent and newly diagnosed oligometastatic (≤3 on bone scan/CT and ≤5 on PSMA PET) men to standard-of-care (ADT+2nd line HT+prostate RT) or standard-of-care + SBRT to all metastases. 2-year radiographic progression is the primary outcome.
• The SPARKLE RCT (primary completion in 2027) in Belgium randomizes oligo-recurrent patients to either (1) MDT alone, (2) MDT+1 mo.of ADT or (3)MDT+6 mo (ADT+enzalutamide). Primary endpoint is 5 new lesions on PSMA PET scan.
• The ADOPT RCT (primary completion in 2022) in The Netherlands randomizes oligo-recurrent patients to either MDT ± ADT. 2.5 yr MFS on PSMA PET scan.

Second opinions

When should I get a second opinion?

In our era of increasing medical specialization, it is sometimes a good idea to get additional medical opinions from experts in specific fields. It is unreasonable to expect any single doctor to know everything. There may be several reasons for seeking a second opinion.

Here are some situations that may lead you to get a second opinion:

• Just a feeling that something doesn’t seem right to you.
• The response to treatment isn’t what you’ve been led to expect
• Your doctor has told you something (or you think he has) that conflicts with information from another doctor or study you’ve read
• You want another opinion regarding a controversial issue (e.g., adjuvant vs salvage radiation, intermittent vs continuous hormone therapy)
• You want to explore a specific new or experimental diagnostic technique or treatment (e.g., CDUS, mpMRI, focal ablation, hyperthermia, etc.)
• You want a more aggressive protocol – something beyond the standard of care.
• You have a rare type of cancer (e.g., neuroendocrine) and want advice from an experienced specialist.
• You want another set of eyes or a confirmation on your biopsy slides, pathology, or radiology results.

The first second opinion we should all get is an expert opinion on our biopsy slides. The pathologist at most hospitals must be a jack of all trades. He has to be able to assess all kinds of tissue samples from cancers as well as all other diseases. Consequently, it would be unreasonable to expect them to be expert at reading a prostate biopsy. It is as much an art as a science, and even practiced pathologists looking at the same slide may differ. Unlike pathology labs in most hospitals, Jonathan Epstein's lab at Johns Hopkins has pathologists who specialize in reading prostate tissue samples. Their opinions are widely held to be definitive. The out-of-pocket cost may be in the $300 range (insurance may not cover it), and it is a simple matter to call your urologist to forward the slides to them. Here is the link.

The other diagnostic technique where a second opinion may change your treatment is multiparametric MRI (mpMRI). There has been a surge in popularity of mpMRIs and they seem to be offered by new facilities every day. The downside is that these are notoriously difficult to read. Experienced “rockstar” radiologists may score them differently from neophytes, and there is considerable inter-observer variability. If you are confident that a “rockstar” read yours, all well and good. If you got yours at a facility that recently began offering them, you may want the DVD sent to a rockstar for a second opinion.

Color Doppler Ultrasound (CDUS) is another imaging technique where years of training make a difference. There is a dynasty of CDUS readers who have mentored pupils starting with Dr. Lee. He taught Dr. Bahn, who taught Dr. Ukimura. I’ve had the opportunity to watch Dr. Bahn in action, and can attest to the artistry involved.

Who do I get second opinions from?

Many of the same techniques mentioned in the blog  “Finding the right doctor,” may be useful in finding the right doctor for a second opinion. 

One aspect to consider is whether you want an opinion from an unrelated doctor at an unrelated institution. If you are suspicious of something your doctor has told you, you may not want him to recommend the doctor for the second opinion. For example, I spoke to a man who had detectable yet stable PSA after his RP. His pathology Gleason score was 6, negative margins, no EPE or SVI. His urologist recommended salvage radiation, and a second urologist at the same practice who took an MRI concurred. He then went to a large tertiary care facility, and an MRI there revealed a “huge” chunk of prostate tissue left behind – something his first urologist failed to mention on the surgery report, and the second urologist did not mention on the MRI report, only noting a small amount of residual tissue. I don’t mean to imply that most urologists are like those two, but I’m only suggesting that an unrelated second opinion has the imprimatur of impartiality.

I think many tertiary care facilities have “tumor boards” that meet periodically to discuss difficult cases. You may be getting the benefit of some of the great practitioners in the field, and also some “out-of-the-box” thinking from experts in related disciplines. This is one of the advantages to treatment at large tertiary care facilities.

How do I tell my doctor?

Doctors are professionals. Approach them with the respect they deserve, and most will respond in kind. I’ve never heard of a doctor objecting to getting a second opinion – they are trained to value them. As long as you don’t take a confrontational stance, he will probably be fine with it. Also, avoid “shopping” until you get the opinion you decided in advance you wanted to hear. Doctors have been known to drop patients for doing that. Just as you expect your doctor to keep an open mind, he has a right to expect the same from you.

Other second-opinion issues

• How do I resolve two conflicting opinions from equal experts? 
• Will my insurance cover it?
• What if my doctor won’t follow the second opinion?
• What if I don’t like the second opinion?

See also:

Finding the Right Doctor

Managing the Doctor/Patient Relationship

Carbon Ion Radiation Therapy for Prostate Cancer

Move over proton, carbon ion is here and the results so far are excellent. Actually, carbon ion radiation therapy has been around for some time, but the cost and the technological requirements have been prohibitive. There are only five treatment centers worldwide, all are government subsidized: three in Japan (Chiba, Hyogo & Gunma), one in Germany (Heidelberg), and one in China (Lanzhou). The newest one built in Gunma, Japan in 2012 took advantage of technological innovations to build a treatment center that is house-sized rather than football-field sized, and at one-third the cost. This brings the cost into line with most proton treatment centers in the US.

Carbon ion offers several radiobiological advantages over protons or photons. The near speed-of-light carbon ions are thousands of times more destructive of cancer cells. It causes multiple irreparable breaks in the DNA of even the most radio-resistant cancer cells. Because the carbon ions do not depend on environmental oxygen to do their cell killing, hypoxia, a low-oxygen condition that can protect cancer cells from proton or photon damage, does not offer a challenge. For this reason, carbon ion, unlike proton, has been used as a monotherapy for high-risk prostate cancer (without combining with X-ray IMRT), and has been found to be effective.

Toxicity is theoretically lower with carbon ions. Compared to protons or photons, it takes much lower doses to have the same effect, and because its Bragg peak effect (at 100%) is greater than protons (at 99%), there is no damage to healthy tissue forward of the beam from failure to stop.  There is greater production of secondary ions from nuclear reactions past the beam, but they have little biological impact. Unlike protons, however, toxic secondary neutrons are not created. Proton therapy often requires the use of spread-out Bragg peaks to treat large-sized volumes like the prostate. This compromises the tissue-sparing advantage of the sharp Bragg peak. However, carbon ions have very high linear energy transfer (LET) and destroy the tumor for a much longer distance within the prostate. This quality is a big advantage in treating organs deep inside the body.

Carbon ions are 12 times more massive than protons. The higher mass means it takes a lot more energy to accelerate a carbon ion beam to the point where it can penetrate deep into the prostate without being absorbed by surface tissues. That’s why it has taken football-field sized cyclotrons to produce the beam. The huge inertia of the beam also makes it more difficult to bend and deliver to the right place in the patient. This requires room-sized gantries with powerful electromagnets. But the upside is that the beam is not easily scattered, as protons are, so the beam goes exactly where it is aimed.

The high relative biological effectiveness (RBE) of the carbon ion beam lends itself well to hypofractionation. As we have seen with HDR brachytherapy, SBRT, and hypofractionated IMRT, prostate cancer is somewhat unique in that it is more efficiently killed by fewer higher doses of radiation (hypofractionation) than by longer courses of lower dose radiation. This quality is called a “low alpha/beta ratio,” which is about 1.5 for prostate cancer cells. Because the alpha/beta ratio of prostate cancer cells is so much lower than most of the healthy tissues of the urinary tract and rectum (with an alpha/beta ratio of about 10), it creates a therapeutic advantage; the total dose for cancer control is much lower than would otherwise be required, and the acute toxicity to healthy tissues is reduced at the same time. Carbon ions have traditionally been delivered as 66 GyE in 20 treatments or fractions. The Chiba Carbon Ion Therapy facility has had successful trials of even greater hypofractionation: 58 GyE in 16 fractions, and 52 GyE in 12 fractions.

It’s one thing to be safe and effective in theory, and quite another to be safe and effective in actual clinical practice. Could the smaller, less expensive Gunma facility replicate the excellent results reported at Heidelberg and Chiba? They prospectively treated 76 patients with 58 GyE in 16 fractions. With median follow up of 51 months, Ishikawa et al. report:

• ·      4-year biochemical relapse-free survival was 95%.
• ·      Grade 2 GI toxicity in 1.3%.
• ·      Grade 2 GU toxicity in 6.6%.
• ·      Patient-reported health-related quality of life was well maintained.

Unfortunately, the authors did not report breakdowns by risk group on this small sample. It would be especially useful to see the effects on sexual function.

For comparison, the larger facility at Chiba reported the following outcomes last year on 1144 patients treated between 2000 and 2012 who had the following characteristics:

• ·      197 were “low risk,” and received no ADT.
• ·      362 were “intermediate risk,” and received 6 months of neoadjuvant ADT.
• ·      585 were “high risk,” and received 6 months of neoadjuvant ADT and at least 18 months of adjuvant ADT.
• ·      Treated with either 66 GyE in 20 fractions or 58 GyE in 16 fractions
• ·      Median age: 68 years.

After median follow up of 49 months, Nomiya et al. report:

• ·      5-yr biochemical relapse-free survival was 91%.
• ·      Grade 2+ GI toxicity was 1.1%.
• ·      Grade 2+ GU toxicity was 6.5%
• ·      Toxicity was less among those treated with the 16 fraction schedule

These results are nearly identical to those reported at Gunma, and are among the lowest we’ve seen for any radiation therapy.

The treatment of high-risk prostate cancer is especially intriguing. Carbon ions seem to be especially effective at treating cancers that are relatively impervious to treatment with X-rays or protons. It is possible that cancer stem cells, neuroendocrine cancer, and hypoxic tumors may be more easily destroyed. In another study from Chiba, Shimazaki et al. reported that with a median follow up of 87 months, the biochemical failure-free rate among high risk patients was 85%. This compares favorably to the 68% rate reported by Memorial Sloan Kettering at 7 years using extra-high dose (86.4 Gy) X-ray IMRT.

The Heidelberg carbon ion treatment facility has only so far reported preliminary results on 14 intermediate risk patients treated with a combination of IMRT (60 Gy in 30 fractions) with a carbon ion boost (18 GyE in 6 fractions) to the prostate. Most (12 of 14) also had neoadjuvant ADT. After a median 28 months of follow up, Nikoghosyan et al. report:

• ·      3-yr biochemical recurrence-free survival was 86%
• ·      No acute Grade 2 GI toxicity
• ·      Acute Grade 2 GU toxicity was 36% and resolved in most (12 of 14) by the time of the first follow up.

The Gunma results so far show that this therapy is both safe and effective, and can be accomplished at lower cost. Japan has already started building several new facilities, which will be coming on-line shortly. This is not a project with great profit-potential for private industry. The capital costs are enormous, and if there are only 12 treatments necessary, the charge per person would have to be unreasonable to recoup costs. None have yet been announced for the US, but given the excellent outcomes, there may be a role for intermediate-risk and especially for high-risk patients.

The US first demonstrated the efficacy of carbon ion treatment at the Lawrence Berkeley National Laboratory in the 1970s and 80s. This was the proof of concept that led Germany and Japan to invest in this treatment. The Dept. or Energy has encouraged renewed US interest, and there is a proposal for a national particle beam R&D center at Walter Reed. The proposed R&D center, which would cost approximately $150M, would exist to advance both research and treatment options for tumors:

• ·      exhibiting a high-risk of local failure post photon (or proton) RT
• ·      radio-unresponsive due to histology, hypoxia, and other factors
• ·      recurring
• ·      efficient at repairing cellular damage
• ·      adjacent to critical normal structures, especially if resection could lead to a substantial loss of organ function.

Starting with a national R&D center may provide the data, technology and cost improvements that private industry would need to justify investment. Perhaps with that, and the enhanced therapeutic ratio of carbon ions, it may make more sense on a cost/benefit basis than the current spate of proton treatment centers.

The synergy of combining radiation and immunotherapy in the treatment of prostate cancer

(updated)

Finkelstein et al have written an excellent review of the current understanding of this emerging and complex field. In contrast to some earlier studies that showed that radiation depressed the gamut of white blood cell types (e.g., Johnke et al, 2005), recent studies have shown that any such radiation-induced leukocyte suppression in high risk men is temporary, and there is a long-lasting enhancement of the anti-cancer immune response. The discrepancy with earlier findings may be due to higher doses of radiation used now, or the higher-precision radiation fields. There is also some evidence that the effect may vary with the kind of prostate cancer, the phenotype, associated with different risk levels, pelvic lymph node radiation, and by the way the dose is given (e.g. LDR brachytherapy vs SBRT). 

In fact, the authors find the opposite of the conventional wisdom to be true: radiation has an immune stimulatory effect when used on men with high-risk prostate cancer. There is an opportunity to bolster this effect when treating high-risk men with radiotherapy -- initial prostate radiation, salvage radiation after surgery, or radiation to isolated metastases. If this effect is maximized, there is a hope of killing off systemic micrometastases and tumors well outside of the radiation field. This is called the abscopal or bystander effect.

Radiation kills cancer cells, and the cellular debris is a source of antigens. Dendritic cells learn to use those antigens to activate killer T cells that then seek out and destroy cancer cells elsewhere that express those antigens. The damaged cancer cells also signal a host of other tumor-toxic molecules to form. Radiation-modified cancer cells that escaped direct annihilation become more immune-susceptible too.

"Immune exhaustion"  has been raised as one reason why the immune system fails at combating cancer. Reducing the tumor burden with SBRT has been found to increase immune response in patients with melanoma.

Provenge, a dendritic cell boost coupled with immune-stimulatory factors, seems to be a perfect companion to radiation. There is a randomized clinical trial (NCT01807065) at the City of Hope to determine whether Provenge's effectiveness is enhanced by radiation to a single metastasis in men with mCRPC. [Update 2019:] Twardowski et al. reported that progression-free survival was 3.7 months among those who received Provenge after SBRT vs. 2.5 months if they received Provenge without SBRT. This did not reach statistical significance (p=0.06) on this small sample (about 25 in each arm).[Update June 2022:] Hannan et al. reported on 20 mCRPC patients who received Provenge and SBRT to 1-5 oligometastatic metastases. The combination did not retard progression compared to historical controls.

(Update 2/2020) A small trial randomized 32 mCRPC patients to Provenge + Xofigo or Provenge alone. Xofigo (radium 223 chloride) is a radioactive drug that destroys bone metastases. After median follow-up of 5.3 months:

• Median progression-free survival was 10.7 months for the combination vs 3.1 months for Provenge alone.
• The % who had a PSA reduction by more than half was 33% for the combination vs 0% for Provenge alone
• The % who had an alkaline phosphatase reduction of more than 30% was 60% for the combination vs 7% for Provenge alone
• There were no increases in side effects for the combination

But immune stimulation will never be longlasting. Eventually, the immune system will regard the cancer cell as if it were a normal healthy cell of one's own and will stop attacking it. To continue the attack, a different sort of immune encouragement is required. These "checkpoint blockers" are currently represented by drugs that have been FDA-approved for use in other cancers: Yervoy (ipilimumab) and Keytruda (PD 1 inhibitor). "Ipi"+ radiation for mCRPC has been tried in two pilot tests. In one, patients were given radiation to a single bone met followed by ipi or a placebo, but the addition of ipi did not significantly increase survival.  In another study, patients were randomly assigned to get ipi+radiation or ipi alone. Both the PSA and the bone met response was good, and about the same for both groups. A larger study in 799 patients of ipi + radiation vs radiation alone confirmed the lack of effect (except in select subgroups) with 10 months of follow-up , but...

(update 8/2020) There was better news after the 799 patients were followed for a longer time. In an update by Fizazi et al 2.4 years later, ipi did increase survival in mCRPC patients, all of whom already had docetaxel, who received a single dose (8 Gy) of radiotherapy (SBRT) to one or up to 5 bone metastases. The effect reversed over time.

• From 0-5 months post-SBRT, survival was 49% worse among those who got ipi
• After 5 months post-SBRT, survival was ⅓ better among those who got ipi
• At 2 years, survival was 25% with ipi vs 17% without ipi
• At 5 years, survival was 8% with ipi vs 3% without ipi
• Ipi drug toxicity caused death in 7 patients
• The effect was the same for those with ≤5 or >5 bone metastases

It may be that those who died in the first few months were already beyond being helped, and the ipi toxicity harmed rather than helped them. Ipi alone has been found to have no effect on survival of mCRPC patients, even when used before docetaxel (see this link). SBRT to bone metastases has not been shown to increase survival (this is the subject of ongoing clinical trials). It is encouraging that the combination has some effect.

(Update 10/6/21) Kwan et al. reported the results of the Phase II ICE-PAC trial combining SBRT of metastases with the immune checkpoint blocker avelumab in 31 mCRPC men in Australia.

• "Disease Control," defined as complete response, partial response, or stable disease, was realized in about half the patients.
• Only 16% suffered serious (Grade 3 or 4) toxicity and only 10% had to discontinue avelumab.
• Response was independent of the number of metastases that were irradiated.

A new immunotherapy, ProstAtak, is being tested with radiation for localized PC (NCT01436968).

Some have suggested that several hypofractionated doses of radiation maximize the immune effect. To that end, UVA initiated a clinical trial (NCT02284971) of an experimental immune stimulant, Varlilumab, coupled with SBRT in 5 doses to the prostate and/or metastases in men with CRPC; however, the trial was terminated due to low accrual.

Other immune stimulants, like Leukine, have been used effectively in mice, and by some clinicians in human patients. It is likely that the optimal immune combo with radiation will include a front-end stimulant and a back-end checkpoint blocker.

Adding androgen blockade may enhance the immune effect still further (Antonarakis & Drake), and radiosensitize the tumors.

There are many unanswered questions:

• Will the abscopal effect be any better in men who are metastatic but still hormone sensitive? 
• Is the abscopal effect maximized with both dendritic cell enhancement and checkpoint blockade, or is the combination too toxic? 
• Does Keytruda work better than Yervoy? 
• What is the optimal timing of radiotherapy and immunotherapy? Should Provenge be used before, during, or after radiotherapy? 
• For how long is the abscopal effect sustained? 
• Is there still an abscopal effect when lymph nodes are irradiated? 
• Does the abscopal effect increase with the number of metastases irradiated? 
• Is there an abscopal effect with Lu-177-PSMA (this is the subject of a clinical trial at UCSF)?
• Will a PARP inhibitor further enhance the abscopal effect? 
• Can the abscopal effect be utilized for rare types of prostate cancer (e.g., neuroendocrine or undifferentiated)? 
• Are there any genomics or biomarkers that are predictive or prognostic? 

written December 25, 2014 and updated since