Head‐to‐head comparison of palbociclib and ribociclib in first‐line treatment of HR‐positive/HER2‐negative metastatic breast cancer with real‐world data from the OPAL registry

Abstract

Cyclin‐dependent kinase 4/6 inhibitors (CDKIs) in combination with endocrine therapy (ET) are the standard‐of‐care in the first‐line treatment of HR‐positive, HER2‐negative metastatic breast cancer. In the absence of direct head‐to‐head trials comparing the efficacy and safety of the different CDKIs, the individual choice of treatment in everyday practice is complex. Inverse probability of treatment weighting was used to emulate a head‐to‐head comparison of palbociclib +ET (PALBO) and ribociclib +ET (RIBO) in patients recruited into the prospective, observational, multicenter registry platform OPAL (NCT03417115). Progression‐free survival (PFS), overall survival (OS) and quality of life surveys were analyzed, also for subgroups stratified by treatment‐free interval (TFI). A total of 623 patients with HR‐positive, HER2‐negative metastatic breast cancer received PALBO (n = 388) or RIBO (n = 235) in their first line of treatment. No difference between PALBO and RIBO was found for PFS (median 26.7 months [23.6, 30.7] vs. 27.0 months [21.1, 30.4], HR 1.01 [0.80, 1.27]) and OS (median 42.4 months [38.8, 50.3] vs. 49.3 months [36.9, NA], HR 0.96 [0.71, 1.28]). There was a trend for longer PFS and OS in patients with TFI <12 months receiving RIBO. Patients reported comparable side effects for both CDKIs. This head‐to‐head comparison revealed no difference in PFS and OS between PALBO and RIBO, however, a trend to longer PFS and OS with RIBO was observed in the subgroup of patients with TFI <12 months. Side effects experienced with PALBO and RIBO highlight the important toxicities to be addressed during treatment decision.