Acute bowel symptoms following relugolix and stereotactic body radiotherapy for localized prostate cancer.

e17086 Background: Androgen deprivation therapy improves cancer control in combination with prostate radiotherapy. Relugolix, an oral GnRH receptor antagonist, achieves rapid profound castration. Both prostate Stereotactic Body Radiotherapy (SBRT) and relugolix can cause burdensome bowel symptoms. This study evaluated the incidence and severity of bowel symptoms following relugolix and SBRT for unfavorable localized prostate cancer. Methods: This prospective study received IRB (#12-1775) approval. Patients were treated at Georgetown per an institutional protocol. Physician reported toxicities were scored using the CTCAE V.4. Patient reported bowel symptoms (urgency, frequency, incontinence, bloody stools and pain) and overall bowel bother were assessed via the Expanded Prostate Index Composite (EPIC)-26 before relugolix initiation, the first day of SBRT, and at each follow-up (3, 6, and 12 months). Responses were grouped into three categories (no problem, very small/small problem, and moderate/big problem). Scores were transformed to a 0-100 scale with higher scores reflecting less bother. All patients were treated with robotic SBRT (Accuray). Items were evaluated for statistical significance (paired t-test, p<0.05) and clinical significance (minimally important difference (MID); 0.5 standard deviations from baseline). Results: From June 2012 to December 2023, 102 localized prostate cancer patients (80 intermediate, 22 high risk) treated with prostate SBRT (35–36.25 Gy) and relugolix (0.89-16.67 months) were included in this study. Median age was 72.1 years (49.4–93.9), 31% were black, and 26% had rectal spacers. Relugolix was initiated for a median of 3.4 months (range, 1.0–9.2) prior to SBRT and completed in a median of 2.9 months (range, 0.3-12.9) post-SBRT. Cumulative incidence of acute grade 2 gastrointestinal toxicity was 9%. There were no acute grade 3 bowel toxicities. EPIC bowel summary scores maximally declined at 3 months post-SBRT (92.8) but this was not statistically or clinically significant (MID = 5.2). There was a statistically but not clinically significant decrease in mean bowel control scores (MID = 2.2, p<0.5) at 3 and 6 months post-SBRT which resolved by 12 months. No individually assessed bowel symptom had clinically significant increases. At baseline, 25% of men reported annoyance due to bowel symptoms with 3% rating it as a moderate to big problem. This increased to 38% at 12 months post-SBRT with 2% rating it as a moderate to big problem. There were no clinically significant increases in overall bowel bother at any follow-up (MID = 9.2). Conclusions: In this cohort, observed proctitis rate and severity following relugolix and SBRT is low. QOL statistically decreased on follow-up, but these results appear similar to those reported for patients treated with SBRT alone, suggesting that relugolix is not contraindicated in patients receiving prostate SBRT.