Real-World Treatment Patterns and Outcomes in Elderly Patients with Metastatic Breast Cancer: A Multi- institutional Retrospective Cohort Study

Background : As populations age worldwide, breast cancer mortality among elderly patients continues to rise despite therapeutic advances. This study investigates differences in treatment patterns and outcomes between elderly and younger patients with metastatic breast cancer. Methods : We analyzed clinical data from the Advanced Breast Cancer Database (ABCD) maintained by the Japanese Breast Cancer Research Group. The dataset included patients registered between June 1, 2020, and October 31, 2023, encompassing clinicopathologic information, treatment details, breast cancer specific survival (BCSS), and overall survival (OS). Results : A total of 1720 patients were included. The frequency of chemotherapy and genomic testing decreased with age, yet patients in their 70s demonstrated treatment durations and survival outcomes comparable to those of younger patients. In contrast, patients aged ≥80 years exhibited significantly shorter duration of second-line therapy (adjusted HR:0.65, 95%CI:0.44-0.98) and poorer OS (adjusted HR:0.62, 95%CI:0.37-1.02) and BCSS (adjusted HR:0.65 95%CI:0.38-1.11), despite most deaths being attributable to breast cancer rather than non–cancer-related causes. Conclusions : This multicenter retrospective study demonstrates that patients in their 70s can achieve comparable benefits from systemic therapy to younger individuals, emphasizing the importance of not withholding treatment based solely on chronological age. Conversely, the limited effectiveness of later-line therapies in patients aged ≥80 highlights the need for individualized treatment strategies that balance efficacy, quality of life, and comorbidities through comprehensive geriatric assessment and shared decision-making.