Real-world outcomes of palbociclib plus endocrine therapy in elderly patients with HR+/HER2- advanced breast cancer in Japan: a subgroup analysis of the P-BRIDGE study by age group

Palbociclib (PAL), a cyclin-dependent kinase 4/6 inhibitor, plus endocrine therapy (ET) is recommended as first-line (1L) treatment for hormone receptor-positive (HR+)/ human epidermal growth factor 2 negative (HER2-) advanced breast cancer (ABC). Despite broad use in real-world clinical settings, few studies have evaluated its effectiveness in elderly patients in Japan. The multicenter, observational P-BRIDGE study included HR+/HER2- ABC patients (N = 693) who initiated PAL + ET as 1L or second-line treatment during 2017–2020 in Japan. Treatment outcomes and patterns were evaluated by age category (< 65; ≥ 65 to < 75; ≥ 75 years). Among patients treated with 1L PAL + ET (N = 426), 266, 118, and 42 patients were aged < 65, ≥ 65 to < 75, and ≥ 75 years, respectively. Patients aged ≥ 75 years were less likely to initiate PAL at 125 mg (64.3%) than patients aged < 65 (95.5%) and ≥ 65 to < 75 (88.1%) years. More patients aged ≥ 75 years discontinued PAL due to adverse events than other age groups. Median real-world progression-free survival (95% CI) was 24.5 months (18.2–30,4), 25.7 months (16.8–36.7), and 45.4 months (20.4–52.4), in the < 65, ≥ 65 to < 75, and ≥ 75-year age groups, respectively. Corresponding median overall survival was 68.2 months (65.0-not reached [NR]), NR (56.3-NR), and 68.0 months (45.8-NR), respectively. The effectiveness of PAL + ET in elderly patients in the real-world setting in Japan appears comparable to other age groups. These findings support PAL + ET as a viable treatment option for all patients, including the elderly, while highlighting the need for close monitoring and individualized treatment strategies, especially in older patients.