PURPOSE Older women with high-risk early breast cancer (EBC) benefit from adjuvant chemotherapy, but their treatment is frequently complicated by toxic side effects, resulting in dose reductions and delays. This makes it challenging for oncologists to maintain a relative dose intensity (RDI) ≥ 85%, as recommended for optimal curative-intent treatment. Understanding which women are at risk of receiving suboptimal RDI may inform treatment discussions and guide early, targeted supportive care or geriatric comanagement interventions. METHODS This was a prespecified secondary analysis of the HOPE trial, which enrolled women age ≥ 65 years with EBC initiating neoadjuvant or adjuvant chemotherapy. RDI was calculated as the ratio of delivered to planned chemotherapy dose intensity. The primary outcome was low RDI, defined as RDI < 85%. Multivariable logistic regression with stepwise selection was used to evaluate the association between baseline variables (demographic, clinical, and geriatric assessment) and low RDI. Survival probability was estimated using the Kaplan-Meier method, and the log-rank test was used to compare overall survival. RESULTS Three hundred twenty-two patients (median age at diagnosis, 70 years; range, 65-86 years) were included. The median follow-up was 4 years. Sixty-six patients (21%) had a low RDI. Age ≥ 76 years (odds ratio [OR], 2.57; 95% CI, 1.12 to 5.91; P = .03), lower performance status (OR, 4.32; 95% CI, 1.98 to 9.42; P < .001), and use of anthracycline-based or cyclophosphamide, methotrexate, and fluorouracil regimens (OR, 3.47; 95% CI, 1.71 to 7.05; P < .001) were associated with low RDI. The 5-year overall survival probability was 0.80 versus 0.91 in patients with RDI < 85 versus ≥ 85%, respectively (log-rank P = .02). CONCLUSION One in five older patients with EBC treated with standard chemotherapy received low RDI and had inferior survival outcomes. Older patients at risk for low RDI should be identified and targeted upfront before initiating chemotherapy.