Factors associated with low chemotherapy dosing in high risk breast cancer.

Abstract

e15520 Background: Chemotherapy dose is often reduced or delayed due to adverse effects. However, a low relative dose intensity (RDI) is associated with reduced disease control and survival. There is little data among patients receiving modern breast cancer regimens regarding the risk of low RDI, or factors associated with it. Methods: We used an institutional registry at a large multidisciplinary cancer center to identify subjects with incident invasive, non-metastatic breast cancer diagnosed between 2009-2018. We focused on a subset of high-risk patients for whom chemotherapy is clearly recommended by guidelines: triple negative (estrogen receptor, progesterone receptor and HER2 negative) or HER2-positive subtypes, and either positive lymph node metastases or tumor size > 1.0 cm. We obtained administration dates and doses for the following agents: doxorubicin, cyclophosphamide, paclitaxel, docetaxel, and carboplatin. Our primary outcome was RDI < 85% of guideline-recommended doses of at least one of these agents. Other outcomes included dose of each agent (first cycle dose < 85% or total dose < 85) and timing (delay ≥7 days or early discontinuation). Variables used for analyses included BMI ≥25, race, HER2 status, age ≥55 years, marital status, stage, and Charlson co-morbidity score. Results: More than half of our cohort of high risk breast cancer patients experienced a low RDI of at least one chemotherapy agent. Out of the 237 patients who met our inclusion criteria, 60% had a low RDI, 10% received a low first cycle dose, 38% received a low total dose, and 46% experienced either a dose delay or discontinued treatment. Using logistic regression analyses, we found that being overweight (CI: 1.01-3.54; p = 0.046) and stage 3 breast cancer (CI:1.05-5.96; p = 0.038) were associated with increased odds of having a low RDI. Low total dose was associated with being overweight (p = 0.0181), unmarried (p = 0.0278), and stage 3 (p = 0.0201). HER2-positive status was also associated with a low first cycle dose (p = 0.001) and dose delays or discontinuation (p = 0.0002). Conclusions: Having a BMI ≥25, higher-stage, or being unmarried, which may serve as a proxy for low social support, are factors that may help identify patients who will have guideline-recommended chemotherapy doses reduced.