OBJECTIVES: Data on impact of National Comprehensive Cancer Network (NCCN) treatment guideline adherence among patients with metastatic breast cancer (MBC) on clinical and economic outcomes is limited. In this study, we examined the impact of guideline-concordant treatment among elderly women with HER2-positive MBC on all-cause mortality, breast cancer-specific mortality, and costs.

METHODS: A retrospective cohort study was conducted using the Surveillance, Epidemiology, End Results-Medicare linked database. The study cohort included women age 66 years and older diagnosed with HER2-positive MBC during 2010-2013. Adjusted Cox proportional hazards models were conducted to evaluate the impact of guideline-concordant treatment on all-cause and breast-cancer specific mortality. A generalized linear model with log link and gamma distribution was conducted to examine the impact of guideline-concordant treatment on average Medicare costs, after adjusting for patient demographic and socioeconomic characteristics, clinical factors, tumor characteristics, healthcare access, and external environmental healthcare factors.

RESULTS: Out of 241 women included in the analyses, 76.8% received guideline-concordant initial treatment. An unadjusted analysis showed that those who received guideline-concordant treatment were more likely to survive longer than those who did not receive guideline-concordant treatment. In adjusted analyses, receipt of non-guideline-concordant treatment was associated with higher hazards of all-cause mortality (hazard ratio (HR)=4.226, 95% confidence interval (CI)=2.932-6.091, p<0.001) and breast cancer-specific mortality (HR=4.061, 95% CI=2.701-6.107, p<0.001) compared to those who received guideline-concordant treatment. There was a significant difference in the average Medicare costs per month between women who received guideline concordant treatment and those who did not ($9,593 vs. $19,432). In an adjusted analysis, the difference reduced but remained significant ($4,766 vs. $9,678, P<0.001).

CONCLUSIONS: Non-concordant care was associated with higher hazards of all-cause mortality and higher Medicare costs per month. Our findings suggest clinical and economic benefit of providing guideline-concordant care among elderly women with HER2 positive metastatic breast cancer.