Abstract
BACKGROUND: Little is known about how use of chemotherapy has evolved in breast cancer patients. We therefore describe chemotherapy patterns for women with stage I-IIIA breast cancer in the Optimal Breast Cancer Chemotherapy Dosing (OBCD) Study using data from KPNC (Kaiser Permanente Northern California) and KPWA (Kaiser Permanente Washington). FINDINGS: Among 33,670 women, aged 18 + y, diagnosed with primary stage I-IIIA breast cancer at KPNC and KPWA from 2006 to 2019, we explored patterns of intravenous chemotherapy use, defined here as receipt of intravenous cytotoxic drugs and/or anti-HER2 therapies. We evaluated trends in chemotherapy receipt, duration over which chemotherapy was received, and number of associated infusion visits. In secondary analyses, we stratified by receipt of anti-HER2 therapies (trastuzumab and/or pertuzumab), given their longer duration. 38.9% received chemotherapy intravenously, declining from 40.2% in 2006 to 35.6% in 2019 (p-trend < 0.001). Among 13,089 women receiving chemotherapy, neoadjuvant treatment increased (4.1-14.7%; p-trend < 0.001), as did receipt of anti-HER2 therapies (20.8-30.9%) (p-trend < 0.001). The average treatment duration increased (5.3 to 6.0 months; p-trend < 0.001), as did the number of infusion visits (10.8 to 12.5; p-trend < 0.001). For those receiving anti-HER2 therapies, treatment duration and average number of visits decreased; among those not receiving anti-HER2 therapies, number of visits increased, with no change in duration. CONCLUSIONS: While the prevalence of chemotherapy receipt has decreased over time, the use of neoadjuvant chemotherapy has increased, as has use of anti-HER2 therapies; duration and number of administration visits have also increased. Understanding these trends is useful to inform clinical and administrative planning.