Association of guideline-concordant initial systemic treatment with clinical and economic outcomes among older women with metastatic breast cancer in the United States.

Purpose: We examined guideline-concordant initial systemic treatment among women with metastatic breast cancer, its predictors, and if guideline-concordant treatment was associated with mortality, healthcare utilization and Medicare expenditures.

Methods: This retrospective observational cohort study was conducted using the Surveillance, Epidemiology, End Results-Medicare linked database. Women aged 66-90 years diagnosed with metastatic breast cancer during 2010-2013 (N = 1282) were included. The National Comprehensive Cancer Network treatment guidelines were used to determine the guideline-concordant initial systemic treatment following cancer diagnosis. A logistic regression analysis was conducted to examine significant predictors of guideline-concordant treatment. Generalized linear regressions were used to examine the association between guideline-concordant treatment and healthcare utilization and average monthly Medicare expenditures.

Results: About 74% of the study cohort received guideline-concordant initial systemic treatment. Women who received guideline-concordant treatment were significantly more likely to be comparatively younger (p < 0.05), were married/partnered (p = 0.0038), had HER2 positive tumors, and had good performance status. Adjusted hazards ratios for all-cause (2.364, p < 0.0001) and breast-cancer specific mortality (2.179, p < 0.0001) were higher for women who did not receive guideline-concordant treatment. Rates of healthcare utilization were also higher for women not receiving guideline-concordant treatment. Average monthly Medicare expenditures were 100.4% higher (95% confidence interval: $77.3%-126.5%) for women who did not receive guideline-concordant treatment compared to those who received guideline-concordant treatment (p < 0.0001).

Conclusion: One fourth of the study cohort did not receive guideline-concordant initial systemic treatment. Guideline-concordant initial treatment was associated with reduced mortality, and lower healthcare utilization and Medicare expenditures in women with metastatic breast cancer.