BACKGROUND: Lasofoxifene, a novel endocrine therapy (ET), showed antitumor activity versus fulvestrant in women with ESR1-mutated, metastatic breast cancer (mBC) that progressed on prior ET (phase 2, ELAINE 1 study). We investigated changes in genitourinary syndrome of menopause (GSM) vulvar-vaginal symptoms with lasofoxifene and how patient/disease characteristics affect baseline vulvar-vaginal symptoms in ELAINE 1. METHODS: Women were randomized to oral lasofoxifene 5 mg/day or IM fulvestrant 500 mg (days 1, 15, and 29, then every 28 days) until disease progression/severe toxicity. Changes in mean vaginal (VAS) and vulvar (VuAS) assessment scales, and their composite (average of all symptom scores/patient), from baseline to week 16, and mean baseline VAS/VuAS scores by patient/disease characteristics, were descriptively summarized. RESULTS: Of 103 enrolled patients, 72 (70%) completed the VAS/VuAS (mean age 61.5 years). Vaginal (40%)/vulvar (25%) dryness and vaginal pain (22%) were the most frequently reported symptoms
26% reported ≥1 moderate/severe symptom. Lasofoxifene decreased the mean composite VAS/VuAS, VAS, and VuAS from baseline to week 16 by 74%, 74%, and 79%, respectively
fulvestrant increased them by 36%, 15%, and 63%, respectively. Baseline vaginal/vulvar symptoms were more severe if patients were under age 40, had no visceral disease, used adjuvant tamoxifen previously, or had longer AI duration in the adjuvant/metastatic settings. CONCLUSIONS: Oral lasofoxifene (5 mg/day), but not fulvestrant, appears to improve GSM vaginal symptoms in women with mBC. These preliminary findings suggest further study is needed
such will be explored in the phase 3, registrational, ELAINE 3 trial in patients with ESR1-mutated, ER+/HER2- mBC.