Low relative dose intensity adjuvant chemotherapy in elderly patients with breast cancer: predictors and impact on survival

Chemotherapy improves outcomes in patients with high-risk early or locally advanced breast cancer, but older adults often experience higher toxicity that leads to treatment delays, dose reductions, and reduced relative dose intensity (RDI). This study examined predictors of low RDI and its impact on overall survival (OS) in women aged over 65 years treated with neoadjuvant or adjuvant chemotherapy at San Juan de Dios Hospital (Costa Rica) between November 2018 and April 2023. A total of 264 patients (mean age: 70.1 years) were included. Nearly one-third had a Charlson Comorbidity Index (CMI) greater than 6. Tumor subtypes were hormone receptor (HR)+/ human epidermal growth factor receptor (HER2)-(48.9%), HR+/HER2+ (15.9%), HR-/HER2+ (33%), and triple-negative (17.8%). Most patients (68.6%) received anthracycline-based regimens. Overall, 17.4% had an RDI below 80%. After a median follow-up of 54.6 months, 56 deaths were recorded. Low RDI was significantly associated with worse OS [hazard ratio: 1.79, 95% confidence interval (CI): 1.02-3.13; P = 0.04]. Independent predictors of low RDI were anthracycline-based therapy [odds ratio (OR): 4.76, 95% CI: 2.17-9.09], CMI greater than 6 (OR: 2.13, 95% CI: 1.02-4.54), and age more than 70 years (OR: 2.38, 95% CI: 1.14-5.01). These findings suggest that advanced age, comorbidities, and anthracycline regimens increase the risk of reduced RDI, which negatively impacts survival. Supportive measures are critical to maintain chemotherapy intensity in older women.