Dr. Vedang Murthy
Results from the trial, called POP-RT, were reported at the European Society for Radiology and Oncology 2020 Online Congress.
“A question that has been plaguing the radiation oncology community for the last 3 or 4 decades is, ‘Should the pelvic nodes be treated prophylactically in patients with high-risk prostate cancer?’ ” said Vedang Murthy, MD, of Tata Memorial Centre in Mumbai, India, who presented the POP-RT trial at the meeting.
“A lot of effort has gone into trying to answer this question,” he added.
Unfortunately, the question has remained unanswered, as neither the RTOG 9413 trial nor the French GETUG-01 trial showed clear evidence of benefit.
To gain some insight, Dr. Murthy and colleagues conducted the POP-RT trial (NCT02302105). The study’s final analysis included 222 men with locally advanced prostate cancer who had node-negative disease based on MRI and PSMA PET, but had a high risk for occult pelvic nodal involvement (20% or greater according to the Roach formula). The median nodal risk for the trial population was 37.8%.
The men were randomized to daily image-guided intensity-modulated radiotherapy to the prostate (68 Gy in 25 fractions to the gland and seminal vesicles) or to the whole pelvis (the former plus 50 Gy in 25 fractions to the pelvic nodes as a simultaneous integrated boost, including the bilateral common iliac, internal and external iliac, presacral, and obturator node groups). All patients also received at least 2 years of androgen-deprivation therapy (ADT).
Efficacy and toxicity
At a median follow-up of 68 months, the 5-year rate of biochemical failure–free survival, the trial’s primary endpoint, was superior with whole-pelvis radiotherapy (WPRT), at 95.0%, relative to prostate-only radiotherapy (PORT), at 81.2% (hazard ratio, 0.23; P < .0001), Dr. Murthy reported.
Disease-free survival was better in the WPRT group than in the PORT group (89.5% vs. 77.2%; HR, 0.40; P = .002), and the same was true for distant metastasis–free survival (95.0% vs. 87.9%; HR, 0.35; P = .01).
Overall survival was 92.5% with WPRT and 90.8% with PORT, a nonsignificant difference (P = .83).
At the time of biochemical failure, disease recurred in the regional pelvic nodes (with or without distant metastases) in just 1 patient in the WPRT group, compared with 15 patients in the PORT group. Recurrences at other sites were similar across the groups.
The WPRT group had a significantly higher rate of late genitourinary toxicity (17.7% vs. 7.5%; P = .03) but not late gastrointestinal toxicity (6.5% vs. 3.8%; P = .4).
There were no grade 4 toxicities, and the groups were similar on patient-reported outcomes.
Explaining the results
Several factors may explain why the POP-RT trial was clearly positive for WPRT, whereas the RTOG 9413 and GETUG-01 trials were not, according to Dr. Murthy.