Abstract PS5-05-01: Treatment Intensity and Survival in Older Adults with Breast Cancer: Undertreatment or Overtreatment?

Abstract Background Older adults with breast cancer are under-represented in clinical trials despite the increasing aging population and extended life expectancy. Concerns about comorbidities and treatment-related toxicity lead to undertreatment. It remains unclear whether reduced treatment intensity leads to inferior survival outcomes, or whether intensive treatment in frail individuals contributes to harm. This study aimed to investigate real-world treatment patterns and their association with survival outcomes in older breast cancer patients. Methods We retrospectively reviewed patients aged ≥65 years who underwent curative surgery for breast cancer at Inha University Hospital between January 2007 and December 2018. Clinical characteristics, treatment modalities (chemotherapy, radiotherapy, endocrine therapy, anti-HER2 therapy), and treatment completion rates were recorded. Disease-free survival (DFS) and overall survival (OS) were compared based on age and treatment receipt and completion using Kaplan-Meier analysis and multivariate Cox regression. Results A total of 278 patients were included (median age 70.0 years). Total mastectomy was performed in 51.1%, and axillary lymph node dissection in 31.2%. For adjuvant therapies, 75.5% received endocrine therapy, 44.2% radiotherapy, 38.1% chemotherapy, and 8.4% anti-HER2 therapy. Treatment completion rates varied, with dropout rates of 31.8% for anti-HER2 therapy, 27.8% for endocrine therapy, and 15.9% for chemotherapy. OS significantly declined with increasing age groups (65-69 vs. 70-74 vs. ≥75), with 7-year OS rates of 96.4%, 94.0%, and 81.1%, respectively (p = 0.011), whereas DFS and breast cancer specific survival did not differ significantly by age. In univariate Cox models, OS was associated with age and treatment factors including chemotherapy and endocrine therapy completion, while DFS was more closely linked to pathologic features including lymphovascular invasion and Ki-67 proliferation index. In multivariate analysis adjusting for stage and endocrine therapy completion, older age (≥75 years) remained independently associated with worse overall survival (OR 1.79, 95% CI 1.01-3.18, p = 0.047). Conclusions While older age was independently associated with worse OS, DFS did not differ by age, indicating that mortality in older patients is more attributable to non-cancer causes, and that appropriately treated older adults can achieve comparable recurrence outcomes. These findings highlight the need for individualized treatment decisions based on functional status rather than chronological age, particularly to avoid undertreatment in fit older adults. Citation Format: S. Lee, S. Park, S. Lim. Treatment Intensity and Survival in Older Adults with Breast Cancer: Undertreatment or Overtreatment? [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS5-05-01.