Phuoc Tho Tran, MD, Examines Efficacy Data for SRT/Enzalutamide Vs Placebo in Advanced Prostate Cancer

At the 2022 American Society for Radiation Oncology (ASTRO) Annual Meeting, CancerNetwork^® spoke with Phuoc Tho Tran, MD, professor and vice chair for Research of Radiation Oncology at the University of Maryland Medical System, about the phase 2 SALV-ENZA trial (NCT02203695). On the trial, patients with high-risk prostate-specific antigen (PSA)–recurrent prostate cancer after radical prostatectomy were treated either enzalutamide (Xtandi) plus androgen deprivation therapy in combination with salvage radiation therapy vs a blinded placebo. The goal of the study was to look at the primary end point of freedom from PSA progression.

Transcript:

This was a multi-institutional study [where patients were stratified] by the center, surgical margin status, whether they had Gleason grade 7 vs 8 through 10 disease, and then PSA [prostate specific antigen] at enrollment. Ultimately, we could only enroll 43 patients per arm, so 86 [patients] total. The primary end point was freedom from PSA progression which we defined as patients who were able to achieve an undetectable PSA. If their PSA reached 0.2 or greater, that was considered a PSA progression event. If they were not able to achieve undetectable PSA following their treatment phase, progression was determined to be an increase of 0.2 above their nadir.

Pre-salvage radiation PSA was 0.3, which is very consistent with patients we see nowadays. The primary end point of the trial was positive for freedom from PSA progression with an HR of 0.42, which was statistically significant. At 2 years, an approximately 20% improvement in the enzalutamide-containing arm [was observed]. The pre-specified subset analysis, which I don’t want to make too large of a point about, [indicated that] patients with T3 or margin-positive disease may benefit more from the addition of enzalutamide compared with placebo.

[When looking at] toxicity, what we found overall is that toxicity between enzalutamide and the placebo was very similar. We’re happy that this was a double-blinded, placebo-controlled trial; the data were very believable. There were some differences [between treatment arms]. There was more breast and nipple tenderness in the enzalutamide-containing arm, but it was only in a quarter of patients and the vast majority of events were grade 1. We also unexpectedly noticed there was a little bit more nausea in the enzalutamide arm in about 20% of patients or so but again, most events were grade 1. Other than that, there was no statistical difference between the enzalutamide arm and the placebo arm; both were very well tolerated.

Reference

Tran PT, Lowe K, Wang H, et al. Phase II randomized study of salvage radiation therapy (SRT) plus enzalutamide or blinded placebo for high-risk PSA-recurrent prostate cancer after radical prostatectomy: the SALV-ENZA trial. Presented at 2022 American Society for Radiation Oncology (ASTRO) Annual Meeting; October 23-26, 2022; San Antonio, TX; Abstract 159. Accessed October 28, 2022.