Abstract PS12-22: Maintenance therapy with everolimus plus aromatase inhibitors vs aromatase inhibitors as after first-line chemotherapy in HR+/HER2- metastatic breast cancer: Updated analyses of the phase III randomized MAIN-A trial

Background Despite endocrine therapy is the mainstay of treatment for HR+/HER2- metastatic breast cancer (MBC), patients with high disease burden or those at risk of visceral crisis are still offered first-line chemotherapy (CT). Chemotherapy is generally followed by maintenance hormonal therapy. The MAIN-A study is an investigator-driven, randomized phase III trial designed to compare maintenance everolimus (EVE) combined with aromatase inhibitors (AI) versus AI alone in pts with disease control after first-line CT.Methods Postmenopausal pts achieving disease control (stable disease, partial response or complete response) after first-line CT were randomly assigned to EVE 10 mg po daily plus AI or to AI alone. Primary aim was PFS in the ITT. We present here overall survival (OS) results and the impact of tumor characteristics on PFS.Results 110 pts were randomized to EVE+AI (n=52) or to AI (n= 58). Primary aim results have been already presented (Guarneri V, ESMO Breast 2019), showing a non-significant prolongation of median PFS in the ITT population for EVE+AI (9.9 mos vs 7.2 mos, HR 0.764, 95% CI 0.501-1.164. Patients with visceral metastases tended to experience shorter PFS as compared with patients with patients with bone/soft tissues metastases (median 11.1 mos vs 6.4 mos, p=0.0746). The levels of estrogen receptor expression (>or Citation Format: Valentina Guarneri, Saverio Cinieri, Maria Vittoria Dieci, Carmelo Bengala, Gabriella Mariani, Giancarlo Bisagni, Antonio Frassoldati, Claudio Zamagni, Laura Orlando, Carlo Alberto Giorgi, Gian Luca De Salvo, PierFranco Conte. Maintenance therapy with everolimus plus aromatase inhibitors vs aromatase inhibitors as after first-line chemotherapy in HR+/HER2- metastatic breast cancer: Updated analyses of the phase III randomized MAIN-A trial [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS12-22.