Everolimus and exemestane for the treatment of metastatic hormone receptor-positive breast cancer patients previously treated with CDK4/6 inhibitor based therapies.

Abstract

1058 Background: The combination of everolimus (EVE) and exemestane (EXE) is approved as second line endocrine therapy for metastatic hormone receptor positive breast cancer (mHRBC) patients who progressed on non-steroidal aromatase inhibitor (NSAI) therapy based on the BOLERO-2 trial. However, none of the patients in BOLERO-2 received prior CDK4/6 inhibitors, which have since become standard of care for metastatic HRBC. As such, the clinical benefit of EVE + EXE in mHRBC patients previously treated with CDK4/6 inhibitors remains unknown. Methods: We reviewed patients ≥18yo with mHRBC treated with EVE + EXE following NSAI alone or NSAI + CDK 4/6 inhibitor at our institution between 2012-2018. Data collected included patient and tumor characteristics, therapies in the metastatic setting, special interest adverse events, and clinical outcomes. The primary objective was comparing PFS for EVE + EXE therapy between patients who received prior CDK4/6 inhibitor therapy and those who did not. Secondary endpoints included overall survival (OS). Patient features were summarized with descriptive statistics and time-to-event measures were estimated using the Kaplan-Meier method. Differences between groups were tested with Fisher’s exact, Kruskal-Wallis, or log-rank test. Results: Thirty-three patients were included in the study; 17 had prior CDK4/6 inhibitor therapy and 16 did not. Subjects that took EVE + EXE for < 28 days were excluded. Patient characteristics, including prior therapies and sites of metastatic disease, were not significantly different. There was no significant difference in PFS (median 5.7 vs 4.7 months, p = 0.890) or OS (median 17.8 vs 11.4 months, p = 0.177) between patients who received prior CDK4/6 inhibitors and those who did not, respectively. Steroid mouthwash use was associated with a reduced incidence of stomatitis. Conclusions: EVE + EXE is well tolerated and shows similar efficacy in metastatic HRBC patients who received CDK4/6 inhibitor therapy and those who did not. There was a non-significant trend towards improved OS in the CDK4/6 inhibitor group that needs to be further evaluated in larger patient cohorts.