Monday, November 26, 2018

Can surgery+radiation+ADT provide equal outcomes to brachy boost therapy +ADT in high risk men?

As we saw (see this link) among men with Gleason 9 or 10, brachy boost therapy (BBT: external beam radiation with a brachytherapy boost to the prostate) was shown to provide better oncological outcomes (10 year metastasis-free survival and 10 year prostate cancer specific survival (PCSM)) compared to surgery (RP) or external beam radiation (EBRT) alone. Some researchers argue that the comparison was unfair. In that study, 43% of the RP patients received adjuvant or salvage radiation, and virtually all of the BBT patients received 1 year of adjuvant ADT. What if ALL of the RP patients were to receive radiation and ADT?

Tilki et al. did a retrospective study to answer that question. They looked at two groups of Gleason 9/10 patients treated at two institutions between 1992 and 2013:

  • 559 men received RP+pelvic lymph node dissection (PLND) at the Martini-Klinik Cancer Center in Hamburg
    • 88 received adjuvant EBRT
    • 49 received adjuvant ADT
    • 50 received both (called MaxRP)
    • Median ADT duration - 8.6 months in 49 men with negative lymph nodes
    • Median ADT duration - 14.5 months in 39 men with positive lymph nodes
  • 80 men received BBT+ADT (called MaxRT) at the Chicago Prostate Center
    • Median ADT duration - 6 months
After 5.5 years of median follow-up for MaxRT and 4.8 years of median
follow-up for those receiving RP, they found that the risk of PCSM compared to MaxRT was:
  • 2.8 times greater for any RP (statistically significant)
  • 0.5 times less for RP+adjuvant EBRT (not statistically significant)
  • 3.2 times greater for RP+adjuvant ADT (statistically significant)
  • 1.3 times greater for MaxRP (not statistically significant)
The 5-year PCSM was:
  • 2% for MaxRT
  • 22% for any RP (significantly higher than MaxRT)
  • 4% for RP+adjuvant EBRT (not significantly different from MaxRT)
  • 27% for RP+adjuvant ADT (significantly higher than MaxRT)
  • 10% for MaxRP (not significantly different from MaxRT)
They computed a 76% chance ("plausibility index") that the PCSM was plausibly the same for MaxRT vs. MaxRP.

Kishan et al. supplied numbers from his study that are more directly comparable. They are shown in the table below.

Study
Tilki
Kishan
Sample size
BBT: 80
RP+EBRT: 88
RP+ADT: 49
RP+EBRT+ADT: 50
BBT: 436
RP+EBRT: 272
RP+ADT: 175
ADT duration (median)
BBT: 6 months
RP (N1): 14.5 mos.
RP (N0): 8.6 mos.
BBT: 12 months
RP (% N1)
44%
17%
5-year % PCSM
RP (any): 22%
BBT: 2%
RP (any): 12%
BBT: 3%
Adjusted PCSM Hazard Ratio compared to BBT:
RP+ADT: 3.2
RP+EBRT: 0.5 (not sig.)
RP+ADT: 3.2
RP+EBRT: 2.0


We see that the two studies are really not comparable in some respects. The Kishan study was much larger, and was done among many of the top institutions. The Hamburg patients had a much higher percent of positive lymph nodes, and their mortality was twice as high as in the Kishan study. The Chicago patients only got half as much ADT vs. the Kishan study. Importantly, the Kishan study found that RP+EBRT had PCSM that was twice as high as BBT, while the Tilki study showed no statistically significant difference.

Another important aspect was not reported in either study - the toxicity of treatment. We know that surgery plus radiation has worse urinary and sexual side effects compared to surgery alone.BBT carries risk of higher late-term urinary side effects compared to EBRT alone.

Until we have a randomized clinical trial of BBT vs MaxRP, we will never have certainty, but for now, the Kishan study better reflects expected outcomes of these therapies at top institutions.