Impact of prior anticancer treatments on palbociclib (PAL) clinical outcomes in patients with hormone receptor-positive/human epidermal growth factor receptor 2-negative (HR+/HER2−) advanced breast cancer (ABC) in real-world settings.

1055 Background: Cyclin-dependent kinase 4/6 inhibitors (eg, PAL) combined with endocrine therapy (ET) is a standard of care for patients with HR+/HER2− ABC. The impact of prior anticancer treatments on clinical outcomes of patients with HR+/HER− ABC treated with palbociclib in routine care is not well known and was investigated in the POLARIS study. Methods: POLARIS is a prospective, observational, multicenter, real-world study in the US and Canada. Enrolled patients were adults (≥ 18 y) with HR+/HER2− ABC who received PAL + ET as standard of care. Real-world progression-free survival (rwPFS) and overall survival (OS) were described by prior treatment. Results: A total of 1250 patients were enrolled. Median age was 64 years (range, 22–97), 67.9% had recurrent disease, and 72.1% received PAL as first-line treatment (1LOT) vs 27.9% as ≥ 2LOT. Prior anticancer therapies (1LOT: adjuvant/neoadjuvant setting; ≥ 2LOT: metastatic setting) were received by 912 patients (73.0%), which included ET-alone (n=254), chemotherapy-alone (n=235), chemotherapy + ET (n=338) or other (n=85). The median follow-up duration was 35.7 months for rwPFS and 39.1 months for OS. In 1LOT, both rwPFS and OS were numerically shorter for patients who received prior chemotherapy (either alone or with ET) when compared with patients who received ET-alone or had no prior therapy (Table). In ≥ 2LOT, patients who received prior chemotherapy-alone or ET-alone had comparable rwPFS, which was numerically longer than for patients with prior chemotherapy + ET; OS was comparable regardless of prior treatment. Conclusions: Overall, patients with HR+/HER2− ABC with prior chemotherapy receipt tended to have shorter clinical benefit. Regardless of LOT, numerically longer rwPFS was achieved in patients who received prior ET-alone. In 1LOT, OS was longer in patients who received prior ET-alone while in ≥ 2LOT, OS was comparable across prior treatment subgroups. Small sample sizes of some ≥ 2LOT subgroups as well as observational nature of the study may limit interpretation. [Table: see text]