Frequency and predictors of insufficient chemotherapy use among stage I-III breast cancer patients by molecular subtype.

Abstract

154 Background: Identification of distinct molecular subtypes has expanded the treatment options for breast cancer, however, chemotherapy remains the common and effective treatment for each subtype. The objective is to compare the frequency and predictors of insufficient chemotherapy use among two subtypes of stage I-III breast cancer patients: luminal A and triple negative breast cancer (TNBC). Methods: We analyzed data from a CDC funded project - Enhancing Cancer Registry Data for Comparative Effectiveness Research (CER) collected by Louisiana Tumor Registry. Women aged < = 70 years, diagnosed in 2011 with stage I-III luminal A or TNBC breast cancer, tumor size > 1cm, were included (N = 1,189). Insufficient chemotherapy (i.e. no chemotherapy use, nonstandard regimen use, and low relative dose intensity (RDI < 85%)) was evaluated respectively. Potential predictors included age, race, insurance, marital status, census tract-poverty, AJCC stage, grade, tumor size, lymph node status, and Charlson comorbidity. Stepwise model selection with p-value for entry at 0.2 and for stay at 0.25 was used to select the most relevant predictors. Results: The frequencies of no chemotherapy use were significantly different (p < .0001) between luminal A (42%, N = 913) and TNBC patients (9%, N = 241). Older age, white race, no insurance, lower stage or grade, and without lymph node involvement were related with no chemotherapy for luminal A patients; older age, not married, and high poverty for TNBC. There were 36% of luminal A and 40% of TNBC patients receiving nonstandard regimen (p = 0.27). Predictors of nonstandard regimen use were increased age, insurance, stage, and grade for luminal A and high poverty level and stage for TNBC. Reduced RDI occurred in 9% luminal A and 10% TNBC patients (p = 0.61). Small cases precluded the prediction model for low RDI. Conclusions: Luminal A patients are less likely to receive chemotherapy than TNBC patients. Low social economic status factors are associated with no chemotherapy use and nonstandard regimens use, especially for TNBC patients.