OBJECTIVES : There is scarce data on the effect of concordance to the National Comprehensive Cancer Network (NCCN) treatment guidelines on clinical and economic outcomes among patients with human epidermal growth factor receptor 2 (HER2)-negative metastatic breast cancer (MBC). The objective of this study was to examine the effect of guideline-concordant treatment among elderly women with HER2-negative MBC on all-cause mortality, breast cancer-specific mortality, and Medicare costs.

METHODS : We performed a retrospective cohort study using the Surveillance, Epidemiology, End Results-Medicare database. Women aged 66 years and older diagnosed with HER2-negative MBC during 2010-2013 were included. We utilized adjusted Cox proportional hazards models to evaluate how guideline-concordant treatment impacted all-cause and breast cancer-specific mortality. We also conducted a generalized linear model with log link and gamma distribution to examine the impact of guideline-concordant treatment on average monthly Medicare costs. The models were adjusted for patient demographic and socioeconomic characteristics, clinical and tumor characteristics, healthcare access, and external healthcare environmental factors.

RESULTS : A total of 1,089 women were included in the analyses, out of which 72.3% received guideline-concordant initial treatment. An unadjusted analysis showed that those who received guideline-concordant treatment survived longer than those who did not receive guideline-concordant treatment. In adjusted analyses, we found that women who did not receive guideline-concordant treatment had significantly higher hazards of all-cause mortality (hazard ratio (HR)=2.143, p<0.001) and breast cancer-specific mortality (HR=1.989, p<0.001) than those who received guideline-concordant treatment. Average monthly Medicare costs among women who received guideline-concordant treatment were significantly lower than those who did not receive guideline-concordant care ($($3,036 vs. $6,172, p<0.0001) in the adjusted analysis.

CONCLUSIONS : More than one quarter of the study cohort did not receive guideline-concordant care. Our findings indicate that providing guideline-concordant cancer treatment to elderly women with HER2-negative metastatic breast cancer can improve their clinical and economic outcomes.