Incidence and Predictors of Low Dose-Intensity in Adjuvant Breast Cancer Chemotherapy: A Nationwide Study of Community Practices

Abstract

Purpose: This retrospective study was undertaken to assess practice patterns in adjuvant chemotherapy for early-stage breast cancer (ESBC) and to define the incidence and predictive factors of reduced relative dose-intensity (RDI). Patients and Methods: A nationwide survey of 1,243 community oncology practices was conducted, with data extracted from records of 20,799 ESBC patients treated with adjuvant chemotherapy. Assessments included demographic and clinical characteristics, chemotherapy dose modifications, incidence of febrile neutropenia, and patterns of use of colony-stimulating factor (CSF). Dose-intensity was compared with published reference standard regimens. Results: Dose reductions ≥15% occurred in 36.5% of patients, and there were treatment delays ≥7 days in 24.9% of patients, resulting in 55.5% of patients receiving RDI less than 85%. Nearly two thirds of patients received RDI less than 85% when adjusted for differences in regimen dose-intensity. Multivariate analysis identified several independent predictors for reduced RDI, including increased age; chemotherapy with cyclophosphamide, methotrexate, and fluorouracil, or cyclophosphamide, doxorubicin, and fluorouracil; a 28-day schedule; body-surface area greater than 2 m 2 ; and no primary CSF prophylaxis. CSF was often initiated late in the chemotherapy cycle. Conclusion: Patients with ESBC are at substantial risk for reduced RDI when treated with adjuvant chemotherapy. Patients at greatest risk include older patients, overweight patients, and those receiving three-drug combinations or 28-day schedules. Predictive models based on such risk factors should enable the selective application of supportive measures in an effort to deliver full dose-intensity chemotherapy.