Real-world effectiveness of palbociclib plus endocrine therapy in HR+/HER2-advanced breast cancer: final results from the POLARIS trial

Background: Strict eligibility criteria for participation in randomized clinical trials (RCTs) often limit the generalizability of data when applied to a more heterogeneous real-world population. Thus, evidence generated directly from real-world populations, including subgroups underrepresented in RCTs, can help inform routine clinical practice. POLARIS (NCT03280303), a prospective, observational, multicenter, cohort study, evaluated patients with hormone receptor-positive/human epidermal growth factor receptor 2-negative (HR+/HER2-) advanced breast cancer (ABC) receiving palbociclib + endocrine therapy (ET) in routine care. Methods: Demographics, baseline characteristics, and treatment patterns were summarized descriptively. Real-world response and clinical benefit rates, real-world progression-free survival (rwPFS), and overall survival (OS) were summarized descriptively by line of therapy and endocrine partner in the overall cohort and various subgroups. Results: Between January 2017 and October 2019, 1250 patients (median age of 64.0 years) initiated treatment with palbociclib-based therapy, including 901 in the first-line (1L) setting and 349 in the second-line or later (>= 2L) settings. Real-world response and clinical benefit rates with palbociclib + ET were 34.0% and 69.4%, respectively, in 1L, and 21.8% and 57.9% in >= 2L. Median rwPFS was 20.9 (95% CI, 18.7-24.7) and 13.5 (10.6-17.1) months, and median OS was 48.5 (42.0-not estimable) and 37.2 (31.2-40.8) months, with 1Land >= 2L palbociclib + ET, respectively. Conclusions: Outcomes in this large, heterogeneous, real-world population are generally consistent with previously reported results from clinical trials and other real-world studies, further supporting the use of palbociclib + ET in patients with HR+/HER2- ABC.