Abstract GS6-02: A randomized, double-blind, placebo-controlled trial of oxybutynin (Oxy) for hot flashes (HF): ACCRU study SC-1603

Abstract Background: HF occur in about 75% of midlife women and are associated with quality of life disruption and premature endocrine therapy discontinuation among breast cancer survivors. Estrogen therapy, effective for HF, is contraindicated in hormone receptor-positive breast cancer (BC). Previous studies have suggested that Oxy could be effective in managing HF. Methods: This randomized, placebo (P)-controlled trial enrolled women who had experienced HF ≥28 times per week over >30 days and of sufficient severity to seek treatment. Patients (pts) were randomized to receive oral Oxy at two doses: 2.5mg BID for 6 weeks (Oxy2.5), 2.5mg BID for a week with subsequent increase to 5mg BID (Oxy5), or matching P, in equal ratios. Baseline and monthly questionnaires were administered including a HF diary, the HF related daily interference scale (HFRDIS) and a symptom experience questionnaire. The primary endpoint was intra-patient change in weekly HF score and frequency from baseline to end of study compared using Kruskal-Wallis tests. Results: 150 pts were accrued between 2/23/2017-3/5/2018. 4 pts cancelled before starting treatment and were excluded from analyses. This interim report includes the first 104 pts for which at least one post-baseline evaluation was available. Baseline characteristics were well-balanced between the arms. Sixty-two percent were on tamoxifen or an aromatase inhibitor for the duration of the study. Pts on both Oxy doses had a significantly greater reduction in HF score and frequency compared to P. Pts on Oxy2.5 had a mean change in HF score of -10 (SD 7.4) vs -5.1 (SD 9.7) with P, p=0.003; and a mean change in average weekly number of HF of -4.6 (SD 3.1) vs -2.3 (SD 3.9), p=0.002. Pts on Oxy5 had a mean change in HF score of -16.2 (SD 5.1) vs -5.1 (SD 9.7) with P, p<0.001; and a mean change in average weekly number of HF of -7.0 (SD 4.0) vs -2.3 (SD 3.9), p<0.001. Repeated measures mixed models confirmed that, after adjusting for baseline values, both Oxy arms had significantly lower HF scores and frequency compared to P (p<0.001). HFRDIS revealed that pts in both Oxy arms experienced improvement in the following HF interference measures: work, social activities, leisure activities, sleep, relations, life enjoyment, and overall quality of life. Pts on Oxy5 also had improvement in HF interference with mood. Pts on Oxy2.5 experienced more stomach pain (p=0.031), diarrhea (p=0.007), nausea (p=0.04), headaches (0.032), episodes of confusion (0.012), dry mouth (p=0.003) and dry eyes (0.027) compared to P. Pts on Oxy5 experienced more constipation (0.004), dry mouth (0.001) and difficulty urinating (0.004) compared to P. There were no differences in study discontinuation due to adverse effects between either Oxy arm and P (Oxy2.5 vs P, p=0.653; Oxy5 vs P, p=0.483). Conclusions: Oxy is superior to P for management of HF. Oxy2.5 and 5 were both associated with significant improvements in HF scores and frequency as well as improvement in HF interference with several quality of life measures. While pts on Oxy experienced more side effects than pts on P, rates of discontinuation due to adverse events were low. This study was supported by the Breast Cancer Research Foundation. Citation Format: Leon-Ferre RA, Novotny PJ, Faubion SS, Ruddy KJ, Flora D, Dakhil C, Rowland KM, Graham ML, Le-Lindqwister N, Loprinzi CL. A randomized, double-blind, placebo-controlled trial of oxybutynin (Oxy) for hot flashes (HF): ACCRU study SC-1603 [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr GS6-02.