(114) Vaginal/Vulvar Symptoms with Lasofoxifene versus Fulvestrant in ESR1-mutated, ER+/HER2- Metastatic Breast Cancer Patients

Abstract Introduction Endocrine therapy (ET), specifically aromatase inhibitors (AIs) that lower estrogen to subphysiologic levels and receptor (ER) degraders non-selectively negatively impact ER function, may induce genitourinary syndrome of menopause (GSM) in breast cancer patients. Novel therapies with positive impacts are desirable. Lasofoxifene reduced incidence a large clinical study, while demonstrating agonist activity on the urogenital system bone trials, including two phase 3 studies postmenopausal women moderate severe vulvovaginal atrophy. is currently under investigation as targeted ET patients disease progression prior for metastatic (mBC) harboring mutations (mESR1). Prevalence vaginal/vulvar symptoms potential endocrine treatments GSM this patient population unclear, thus data were gathered from one largest lasofoxifene assess its area. Objective To investigate changes versus fulvestrant mESR1, ER+/HER2- mBC ELAINE 1. Methods Women multinational (US, Canada, Israel), 2, 1 study randomized oral 5 mg (daily) or IM 500 (days 1, 15, 29, then every 28 days), until progression/severe toxicity. Vaginal/vulvar evaluated an exploratory endpoint using vaginal (VAS) vulvar (VuAS) assessment scales, instruments validated dryness, soreness, irritation, pain 4-point scale (0=none, 1=mild, 2=moderate, 3=severe). English-speaking completed VAS/VuAS at baseline 8 weeks progression. Changes mean composite score (average all reported scores patient) most bothersome symptom (the greatest over 16 treatment analyzed. Results Of 103 enrolled patients, 39/52 (75%) 33/51 (65%) VAS/VuAS; 9/39 (23%) 10/33 (30%) had ≥1 moderate/severe symptom, respectively (Table). Among those who (median age 61.5 years), changed week by −74% +36% patients; −65% −5% fulvestrant. In baseline, percent −72% +32% Conclusions analysis unselected symptoms, mg/day numerically improved relative fulvestrant, albeit small sample size. Baseline prevalence (20–30%) appears have been under-reported population, which be due minimizing less important than control being embarrassed communicate sexual concerns their oncologists. Further warranted evaluate benefits health cancer. Disclosure Yes, sponsored industry/sponsor: Sermonix Pharmaceuticals. Clarification: Industry initiated, executed funded Any authors act consultant, employee shareholder industry for: