Impact of chemotherapy relative dose intensity on cause-specific and overall survival for stage I-III breast cancer: ER+/PR+, HER2- vs. triple-negative

PURPOSE: To investigate the impact of chemotherapy relative dose intensity (RDI) on cause-specific and overall survival for stage I–III breast cancer: estrogen receptor or progesterone receptor positive, human epidermal-growth factor receptor negative (ER+/PR+ and HER2−) vs. triple-negative (TNBC) and to identify the optimal RDI cut-off points in these two patient populations. METHODS: Data were collected by the Louisiana Tumor Registry for two CDC-funded projects. Women diagnosed with stage I–III ER+/PR+, HER2− breast cancer, or TNBC in 2011 with complete information on RDI were included. Five RDI cut-off points (95, 90, 85, 80, and 75%) were evaluated on cause-specific and overall survival, adjusting for multiple demographic variables, tumor characteristics, comorbidity, use of granulocyte-growth factor/cytokines, chemotherapy delay, chemotherapy regimens, and use of hormone therapy. Cox proportional hazards models and Kaplan–Meier survival curves were estimated and adjusted by stabilized inverse probability treatment weighting (IPTW) of propensity score. RESULTS: Of 494 ER+/PR+, HER2− patients and 180 TNBC patients, RDI < 85% accounted for 30.4 and 27.8%, respectively. Among ER+/PR+, HER2− patients, 85% was the only cut-off point at which the low RDI was significantly associated with worse overall survival (HR = 1.93; 95% CI 1.09–3.40). Among TNBC patients, 75% was the cut-off point at which the high RDI was associated with better cause-specific (HR = 2.64; 95% CI 1.09, 6.38) and overall survival (HR = 2.39; 95% CI 1.04–5.51). CONCLUSIONS: Higher RDI of chemotherapy is associated with better survival for ER+/PR+, HER2− patients and TNBC patients. To optimize survival benefits, RDI should be maintained ≥ 85% in ER+/PR+, HER2− patients, and ≥ 75% in TNBC patients.