Disparities in Guideline-Concordant Initial Systemic Treatment in Women with HER2-Negative Metastatic Breast Cancer: A SEER-Medicare Analysis

Background: Data on guideline-concordant initial systemic treatment among women with HER2-negative metastatic breast cancer (MBC) are limited. We determined the proportion of women with HER2-negative MBC who received guideline-concordant treatment and the extent to which independent variables explained differences in guideline-concordant treatment by hormone receptor (HR) status. Methods: We conducted a retrospective cohort study using the SEER-Medicare database. We included women age >65 years diagnosed with HER2-negative MBC during 2010-2013. We used the National Comprehensive Cancer Network treatment guidelines to determine guideline-concordant initial treatment within the first 6 months of a cancer diagnosis. We conducted a multivariable logistic regression to identify the significant predictors of guideline-concordant treatment and a non-linear decomposition method to examine disparities by HR status. Results: Among 1089 eligible women, 72.3% received guideline-concordant treatment. Compared to women who did not receive guideline-concordant treatment, women who received guideline-concordant treatment were more like to be comparatively older (p<0.05), married (p=0.0171), resided in areas with higher proportion of people age >= 25 years with at least four years of college education, and had positive HR status (p<0.0001). Approximately 8% of the disparity in guideline-concordant treatment by HR status was explained by their observed characteristics. Need-related factors explained the highest proportion (66.9%) of the disparity. Conclusion: Our findings indicate improvement of care for older women, who are single/divorced, have negative HR status, and who live in area with lower education levels. Unexplained disparities in guideline-concordant treatment by HR status can be attributed to patient preferences for treatment, physician-level factors, and perceptions.