Background: Breast cancer is now recognized as a heterogeneous disease with distinct biological molecular subtypes which have different prognoses and treatment options. We conducted the first statewide, population-based study to examine systemic treatment among invasive breast cancer (IBC) patients by subtype and determined their associated factors with treatment.

Methods: We analyzed data from the Louisiana Tumor Registry (LTR) and a Centers of Disease Control and Prevention (CDC)-funded special project of Enhancing Cancer Registry Data for Comparative Effectiveness Research (CER), which included Louisiana women diagnosed with microscopically-confirmed invasive breast cancer in 2011. Patient's socio-demographics, tumor characteristics and detailed information on the treatment, including chemotherapy, hormone, radiation and targeted therapy received within 12 months of diagnosis were collected from hospitals, radiation facilities, and medical oncology clinics. Systemic treatments received by each subtype were examined. Univariate and multivariate logistic regression analyses were used to identify factors associated with not receiving systemic treatment. Analyses were carried out using SAS version 9.4.

Results: About 70% of patients were hormone receptor (HR)+/ human epidermal growth factor receptor 2 (HER2)-, 15% triple negative (HR-/HER2-), 10 % HR+/HER2+ and only 5% HR-/HER2+. Among IBC patients with known HR and HER2 status, 72-78% with HR+ had hormonal therapy, 61-75% with HER2+ had Herceptin. About 0.5-6.1% of patients were given therapies which are contradictory to HR/HER2 status and 11-23% of IBC patients with known molecular subtypes did not receive any systemic treatment. Factors associated with not receiving systemic therapy include triple negative subtype and age >65 years. Patients younger than 50 years and with more advanced stages were more likely to receive systemic treatment. Race/ethnicity, grade, lymph node involvement, and comorbidity were not associated with receiving systemic treatment, adjusting for other covariates.

Conclusions: About 12-29% of breast cancer patients in our data set were not receiving treatment consistent with their HR/HER2 status or treatment guidelines. Some possible explanations may be advancing age, death prior to therapy and refusal by patients and/or family. Race, lymph node status and comorbidity were not associated with receiving systemic therapy after adjusting for other covariates. Further studies are needed to explore reasons why patients are not receiving therapy that is concordant with the guidelines and the access to care.

Citation Format: Loch MM, Zhang L, Hsieh M-C, Wu X-C, Chen VW. A statewide, population-based study of molecular subtypes of female breast cancer: Treatment and associated factors. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P1-07-14.