Guideline-concordant treatment among elderly women with HER2-positive metastatic breast cancer in the United States
Background: It is crucial to identify whether women with HER2-positive (HER21) metastatic breast cancer (MBC) are treated according to treatment guidelines and whether treatment disparities exist. This study examined guideline-concordant treatment among women with HER21 MBC and determined the magnitude of differences in treatment between those with positive and negative hormone receptor (HR) status using a nonlinear decomposition technique. Methods: A retrospective observational cohort study was conducted using the SEER-Medicare linked database. The study cohort consisted of women aged $66 years diagnosed with HER21 MBC in 2010 through 2013 (n5241). Guideline-concordant initial treatment after cancer diagnosis was defined based on the NCCN Clinical Practice Guidelines in Oncology for Breast Cancer. A multivariable logistic regression was performed to identify significant predictors of guideline-concordant treatment. A postregression decomposition was conducted to identify the magnitude of disparities in treatment by HR status. Results: Of 241 women included in the study, a total of 76.8% received guideline-concordant treatment. These women were significantly more likely to have positive HR status (P5.0298), have good performance status (P5.0009), and more oncology visits (P,.0001). With 1-year increments in age at cancer diagnosis, the likelihood of receiving guideline-concordant treatment reduced by 5% (P5.0356). The decomposition analysis revealed that 19.0% of the disparity in guideline-concordant treatment between women with positive and negative HR status was explained by differences in their characteristics. Enabling characteristics (marital status, income, and education) explained the highest (22.8%) proportion of the disparity. Conclusions: Nearly one-quarter of the study cohort did not receive guideline-concordant treatment. Our findings suggest opportunities to improve cancer care for elderly women with negative HR status who are unpartnered or have lower socioeconomic status. The high unexplained portion of the disparity by HR status can be due to patient treatment preferences, propensity to seek care, and organizational and physician-level characteristics that were not included in the study.