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Top Line: Can enzalutamide be used in lieu of ADT in men receiving salvage radiation to the prostate fossa?
The Study: When we talk about ADT during salvage radiation for prostate cancer, we typically mean medical therapy to suppress testosterone production. Alternatively, antiandrogen therapy can be used. This was the approach in the landmark RTOG 9601 trial. Enzalutamide is a second generation antiandrogen commonly used in metastatic prostate cancer that has a more appealing profile than bicalutamide. SALV-ENZA was a randomized, phase 2 trial where 86 men with resected, high risk, node negative prostate cancer and a rising PSA (0.05-0.7) received salvage radiation (66.6-70.2 Gy in 37-38 fractions) to the prostate fossa (no nodes) with or without 6 months of enzalutamide. Prior to enrollment they were staged with CT and bone scan (no advanced imaging). The primary outcome was freedom from PSA progression (0.2 increase from post-RT nadir). At 2 years, the addition of enzalutamide significantly improved (or delayed) the rate of FFPP from 66% to 84%. The side effect profile of enzalutamide was favorable with grade 1-2 nipple tenderness (25.6% v 0%) and nausea (18.7% v 0%) significantly more common in the enzalutamide arm. Fatigue, hot flashes, and sexual dysfunction were notably similar between arms. Subgroup analysis suggested those with pT3b disease or R1 resection gained the most benefit from enzalutamide.
TBL: While larger trials are needed, enzalutamide monotherapy in lieu of ADT with salvage prostate fossa radiation appears to improve biochemical control with a favorable side effect profile. | Tran, J Clin Oncol 2022