Abstract P6-18-01: Treatment benefit of ribociclib + letrozole in patients with de novo disease and visceral metastases from the MONALEESA-2 study

Abstract

Abstract Background: Ribociclib (ribo) + letrozole (LET) demonstrated efficacy and safety in first-line treatment of patients (pts) with hormone receptor–positive (HR+), HER2− advanced breast cancer (ABC). Most endocrine therapy (ET)–naive pts with de novo ABC respond to ET, but first-line monotherapy with ET or fulvestrant elicited only moderate efficacy in the FALCON study of pts with visceral metastases (mets). Visceral mets are associated with poor prognosis and may warrant novel treatment options in addition to ET. Here, we present clinical outcomes of treatment with ribo in pts with de novo ABC and visceral mets. Methods: In the MONALEESA-2 study, postmenopausal women with HR+, HER2− ABC (N=668) were randomized (1:1) to receive either ribo 600 mg/d or placebo (3 wk on/1 wk off) + LET 2.5 mg/d (continuous). The primary endpoint was median progression-free survival (mPFS). Results: All pts in this analysis (n=227) had de novo ABC; 108 pts had visceral mets (ribo, n=53; placebo, n=55). Baseline characteristics were similar between the ribo and placebo groups. The median follow-up time was 26.4 months. In pts with visceral mets, mPFS was significantly higher in the ribo group (30.3 months) than in the placebo group (14.1 months; hazard ratio, 0.52; 95% CI, 0.295–0.905; P=0.019). Rates of PFS in these pts in the ribo vs placebo group, respectively, were 76% vs 60% at 12 months and 60% vs 36% at 24 months. Among the pts with visceral mets, clinical benefit rate (CBR) was 79% vs 71% in the ribo vs placebo group, and overall response rate (ORR) in pts with measurable disease at baseline was 55% vs 46%, respectively. In pts without visceral mets (ribo, n=61; placebo, n=58), PFS rates in the ribo vs placebo group, respectively, were 87% vs 72% at 12 months and 66% vs 51% at 24 months. Safety results were consistent with the overall population, and responses were durable with ribo + LET irrespective of whether the pts had visceral or nonvisceral mets. Conclusions: Clinical outcomes from this analysis of the MONALEESA-2 study are consistent with those of the overall population, and ribo + LET prolonged the mPFS and improved ORR and CBR in pts with de novo ABC with visceral mets vs placebo + LET. Citation Format: O'Shaughnessy JA, Arteaga CL, Hart LL, Lindquist DL, Beck JT, Purkayastha DD, Caria N, Hortobagyi GN. Treatment benefit of ribociclib + letrozole in patients with de novo disease and visceral metastases from the MONALEESA-2 study [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 P6-18-01.