# 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

## TL;DR

This study shows that palbociclib plus endocrine therapy is effective for elderly Japanese patients with advanced breast cancer, similar to younger patients, though older patients may need closer monitoring.

## Contribution

The study provides real-world evidence on palbociclib's effectiveness in elderly Japanese patients with HR+/HER2- advanced breast cancer.

## Key findings

- Elderly patients (≥75 years) had comparable progression-free survival to younger patients on palbociclib plus endocrine therapy.
- Older patients were more likely to discontinue treatment due to adverse events compared to younger age groups.
- Median overall survival was similar across all age groups, suggesting palbociclib plus endocrine therapy is viable for elderly patients.

## Abstract

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.

The online version contains supplementary material available at 10.1007/s12282-025-01812-5.