Bothersome hot flashes following relugolix and stereotactic body radiotherapy for localized prostate cancer.

e17087 Background: Androgen deprivation therapy (ADT) has been shown to improve cancer control when combined with radiation therapy. Relugolix is an oral GnRH receptor antagonist that achieves rapid profound testosterone suppression. ADT cause several hormonally related symptoms that resolve with testosterone recovery. Hot flashes are particularly bothersome. This prospective study sought to evaluate the timeline of hot flashes following initiation of a short course of Relugolix and stereotactic body radiotherapy (SBRT) for unfavorable localized prostate cancer. Methods: Institutional IRB (IRB #12-1775) approval was obtained for retrospective review of prospectively collected data. Patients were treated at Georgetown between per an institutional protocol. Hot flashes were self-reported via question 13a of the Expanded Prostate Index Composite (EPIC)-26 prior to ADT initiation, the first day of SBRT, and at each follow-up (1-, 3-, 6-, 9-, and 12-months). The responses were grouped into three relevant categories (no problem, very small-small problem and moderate to big problem). Scores were transformed to a 0-100 scale with higher scores reflecting less bother. All patients were treated with the robotic SBRT (Accuray). Total Testosterone levels were measured at each follow-up. Items were evaluated for statistical significance (paired t-test, p <0.05) and clinical significance (minimally important difference (MID); 0.5 standard deviation from baseline). Results: 89 localized prostate cancer patients (20 intermediate risk, 63 high risk, and 6 recurrent) at a median age of 71.5 years (range 49-89 years) who were treated with prostate SBRT (35-36.35 Gy) and a course relugolix of average length of 6.25 months (range 3-29 months) from January 2021 to September 2023 at a single institution were included in this study. Thirty seven percent were non-white and 24% were obese. Patients initiated relugolix a median of 3 months (range, 0-11) prior to SBRT and completed relugolix a median of 2 months (range, 0-36 months) post-SBRT. Prior to relugolix initiation, 1.3% of men reported hot flashes that were a moderate to big problem. That proportion peaked at 1-month post-SBRT (46.2%) before returning to baseline at 9 months post-SBRT (0%) with a cumulative incidence of 57%. The median baseline EPIC-26 hot flash score of 98.7 declined to 49.0 at 1-month post-SBRT and returned to baseline by 9-months post-SBRT. These differences were statistically (P < 0.01) and clinically significant (MCID = 98.8 +/- 4.45). Testosterone recovery (> 230 ng/dL) occurred in 97% of patients 12 months post-SBRT. Conclusions: Bothersome hot flashes occur in greater than 50% of men treated with short course relugolix and SBRT. Resolution of hot flashes occurs in the majority of men by 9 months post SBRT. Hot flash resolution mirrored testosterone recovery. Reassurance of the temporary nature of hot flashes may reduce patient anxiety and limit associated bother.