Overall survival with palbociclib (PAL) plus an aromatase inhibitor (AI) versus AI alone in older patients (pts) with de novo, HR+/HER2-metastatic breast cancer

Abstract

Cyclin-dependent kinase 4/6 inhibitor in combination with endocrine therapy (CDK4/6i) is the current standard of care in first line (1L) treatment for hormone receptor–positive and human epidermal growth factor receptor 2-negative (HR+/HER2–) metastatic breast cancer (mBC). Comparative effectiveness evidence assessing overall survival (OS) outcomes are limited, particularly in older pts. Our primary objective was to compare OS in Medicare pts treated with 1L PAL + AI versus AI alone in the current SEER dataset. Methods: We conducted a retrospective analysis of HR+/HER2–mBC pts using the SEER-Medicare database. Medicare-enrolled pts aged ≥65 years diagnosed with de novo HR+/HER2– mBC between February 1, 2015, and December 31, 2019 were included. Pts were followed from the start of 1L therapy line until death, Medicare disenrollment, enrollment in a health maintenance organization plan, or the end of available study follow-up (December 31, 2020), whichever came first. Stabilized inverse probability of treatment weighting (sIPTW) was the primary method used to balance patient characteristics at baseline, with propensity score matching (PSM) and multivariable CPH regression as sensitivity analyses. Median OS and the hazard ratio (HR) were estimated using the weighted Kaplan-Meier (KM) method and the weighted Cox proportional hazard (CPH) regression model, respectively. Results: Of 779 included pts, 296 received PAL+AI and 483 received AI alone. Median follow-up was 23.9 months for the PAL+AI arm and 18.2 months for the AI alone arm. After sIPTW adjustment, median OS was 37.6 months (95% CI=34.8-42.0) for PAL+AI vs 25.5 months (95% CI=22.0-28.9) for AI alone (HR=0.73, 95% CI=0.59-0.91). Results from the PSM and CPH regression analyses were consistent with the primary analysis. Key patient characteristics are presented (Table). Conclusions: This comparative effectiveness study showed that PAL+AI was associated with significantly prolonged OS vs AI alone in the 1L treatment of older pts with de novo HR+/HER2- mBC treated in US clinical practice using the SEER-Medicare database. Our results add to the body of evidence on the survival benefit of PAL+AI in this population.