Abstract P1-16-04: Capecitabine efficacy after progression on endocrine treatment and cycline-dependant-kinase 4/6 inhibitor combination in metastatic hormone-receptor positive breast cancer

Abstract

Abstract Background Capecitabine is an oral chemotherapy and often a favoured option in metastatic hormone-receptor positive (HR+) breast cancer (BC) progressing under endocrine therapy (ET). As reported in the BOLERO-6 trial, median time to treatment failure of capecitabine after ET is 6.2 months. Addition of cycline-dependant-kinase 4/6 inhibitors (CDKi) to ET improved survival outcomes in metastatic HR+ BC, thus this combination is the new standard of treatment in metastatic first or second-line setting. Evaluation of capecitabine efficiency after the combination ET - CDKi remains scarce in the literature. This retrospective study aims at describing capecitabine efficacy after disease progression under this combination therapy. Methods Fifty-six Patients, with a 62-year median age (IC95% 42-81), were treated with capecitabine after disease progression under ET - CDKi combination between January 2016 and December 2020. For 46% of them combination therapy was used in first-line setting. Twenty-five patients had exclusive bone metastasis while fifteen had hepatic metastasis. Median follow-up since capecitabine initiation was 13.5 months. Primary endpoint was time to treatment failure (TTF). Second endpoints were progression-free survival (PFS) and overall survival (OS). Univariate and multivariate Cox logistic regression were used to identify survival-associated factors : age < versus ≥ 50 years, hormone-receptor status ER+/PR+ versus ER+/PR-, exclusive bone versus visceral metastases, first line versus second line of CDKi - ET combination, aromatase inhibitor versus fulvestrant. Results Time to treatment failure of capecitabine after combination of CDKi - ET was 6.1 months (IC95% 1.3-17.4). Six patients discontinued capecitabine due to toxicity. Median PFS and OS were respectively 7.1 and 13.4 months. Outcomes were not significantly different regardless of age, hormone receptor status, metastases localization, line of CDKi and ET class, (Table 1). Conclusion In comparison with capecitabine efficacy after ET progression without CDKi in BOLERO-6 trial (TTF = 6,2 months and PFS = 9,6 months), our results suggest that capecitabine efficacy is maintained after progression on combination of ET - CDKi. This efficacy is independent of metastatic sites, and previous ET - CDKi line setting. Table 1.Univariate analysis considering factors of capecitabine time to treatment failureUnivariate analysisVariablesEvent (n)No event (n)pAge (years)0.6Hormone-receptor status n (%)0.3PR+/ER+2917PR-/ER+ or PR+/ER-82Metastasis localisation n (%)Bone metastasis only1690.2Visceral metastasis only71Endocrine therapy n (%)Aromatase inhibitor1240.3Fulvestrant2415CDK 4/6 inhibitor n (%)Palbociclib33160.6Ribociclib/Abemaciclib43CDK 4/6 inhibitor plus ET n (%)First line1790.9≥ 2 lines2010 Citation Format: Capecitabine efficacy after progression on endocrine treatment and cycline-dependant-kinase 4/6 inhibitor combination in metastatic hormone-receptor positive breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P1-16-04.