Stereotactic body radiation therapy (SBRT) is the treatment of choice because it is precise, as well as convenient for the patient (usually completed in 1-5 treatments). It is important to distinguish between two different situations that may involve oligometastases:
- Metastasis-directed SBRT after primary treatment (prostatectomy or prostate radiation) and any local salvage radiation has failed. This is sometimes called "metachronous" treatment of recurrent prostate cancer.
- Radiation to the prostate and oligometastases in newly-diagnosed men, or men who are radiation- or surgery-naive but have progressed to castration-resistance.
- Radiation to metastases for the purposes of pain palliation, or to prevent fractures or spinal compression.
Phuoc Tran is the lead investigator of the "ORIOLE" RCT (NCT0268058) at Johns Hopkins described at this link. It is a small, Phase 2 trial for men in situation A described above. It has some noteworthy characteristics:
- 36 men will receive SBRT, 18 men will receive standard-of-care treatment
- Oligometastases are diagnosed by bone scan and CT
- Patients will be balanced based on whether initial treatment was surgery or radiation, whether they've had hormone therapy, and whether the PSA doubling time was less than 6 months.
- The primary outcome will be radiographic or PSA progression (by >25% over nadir and by > 2 ng/ml) after 6 months.
- To be deemed successful, the treatment will have to reduce this measure of progression by 50%
- identification of additional metastases using the DCFPyL PET/CT
- toxicity of treatment reported by doctors
- pain palliation reported by patients
- local control of metastases (see below)
- Number of circulating tumor cells (CTC)
- Genomic analysis of CTCs
- Immune (T cell) response to treatment
- Time until patients have to start life-long hormone therapy
It may seem odd that detection of fewer than 5 metastases by the DCFPyL PET/CT (developed at Johns Hopkins and now in expanded trials) is not a qualifying criterion. Perhaps they will change that for the Phase 3 trial. Or perhaps they want to prove the concept with a bone scan/CT because it will be several years before that PET scan (so far, the most accurate) is widely available and covered by insurance or Medicare. If it works for bone scan/CT-detected oligometastases, it will certainly work for DCFPyL PET-detected metastases.
Update (August 2017): Dr. Tran has made the following change in protocol:
We did change the criteria recently to allow men who had detectable disease on DCFPyL to enroll on the trial, BUT only if the DCFPyL did not show anything more than what is visible on conventional CT-AP and bone scan. Our thought was that this would allow some patients of the "future" if you will (as PSMA-targeted imaging will be the SOC in 3-5 years) to be included on the trial, but because we do not allow men on the trial with DCFPyL scans that show us more than what is on conventional , we feel that still holds to original concept.
It is also important to note what is not an objective of this early clinical trial. The outcome we most want to know is whether SBRT treatment of metastases extends overall survival. This 6-month trial will not tell us that. There is no doubt that local control will be excellent, but stopping the progression of 1-3 metastases does not necessarily mean that the cancer has been slowed down systemically at all. Certainly, PSA will fall as an immediate result of treatment. For those who are used to monitoring PSA as a measure of their cancer's systemic progression, this can be confusing. It's worth taking a moment to recall what serum PSA comes from in detectably metastatic disease. PSA is a protein on the surface of prostate cancer cells (and healthy prostate cells too.) It doesn't leak out into the blood from prostate cancer unless a tumor forms with its own blood supply. Tumor blood supply tends to be leaky, and so PSA is detected in the blood serum. Larger tumors with more blood supply put out more PSA. So irradiating those tumors and shrinking them is likely to eliminate the PSA they put out. But what about the micrometastases that do not yet have appreciable blood vessels? If there are thousands of them, will it matter that serum PSA was reduced for 6 months? No one knows the answer to that question and this Phase 2 study will not provide the answer. I hope they will provide radiographic progression-free survival separate from PSA progression-free survival.
For the answers to our most important questions we will have to look forward to the outcomes of some of the other RCTs that have longer follow-up than 6 months.
- The CORE RCT (active, no longer recruiting) at Royal Marsden Hospital in London will have 5 years of follow-up (completion in 2024), and will include freedom from widespread metastatic disease and overall survival among the outcomes looked at.
- The STOMP RCT at University Hospital in Ghent had 2 years of follow-up looked at time to lifelong hormone therapy as its primary outcome (reviewed here).
- The PCX IX RCT (among castration-resistant patients) at Jewish General Hospital in Montreal will have 5 years of follow-up (primary outcome in 2025) and has radiographic progression-free survival as its primary outcome.
- The French RCT (recruiting, study completion in 2022) will look at radiographic progression-free survival with follow-up up to 3 years.
- The FORCE RCT at the University of Michigan (primary completion in 2022) 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 in among men with mCRPC as it is in men with newly recurrent disease.