Cardiac Monitoring During Adjuvant Trastuzumab-Based Chemotherapy Among Older Patients With Breast Cancer

Abstract

Purpose Patients treated with adjuvant trastuzumab require adequate cardiac monitoring. We describe the patterns of cardiac monitoring and evaluate factors associated with adequate monitoring in a large population-based study of older patients with breast cancer. Patients and Methods Patients age 66 years or older with full Medicare coverage, diagnosed with stage I to III breast cancer between 2005 and 2009, and treated with adjuvant trastuzumab-based chemotherapy were identified in the SEER-Medicare and the Texas Cancer Registry-Medicare databases. The adequacy of cardiac monitoring was determined. Chemotherapy, trastuzumab use, cardiac monitoring, and comorbidities were identified by using International Classification of Diseases, 9th revision and Healthcare Common Procedure Coding System codes. Prescribing physician characteristics were also evaluated. Analyses included descriptive statistics and multilevel logistic regression models. Results In all, 2,203 patients were identified; median age was 72 years. Adequate monitoring was identified in only 36.0% of the patients (n = 793). In the multivariable model, factors associated with optimal cardiac monitoring included a more recent year of diagnosis (hazard ratio [HR], 1.83; 95% CI, 1.32 to 2.54), anthracycline use (HR, 1.39; 95% CI, 1.14 to 1.71), female prescribing physician (HR, 1.37; 95% CI, 1.10 to 1.70), and physician graduating after 1990 (HR, 1.66; 95% CI, 1.29 to 2.12). The presence of cardiac comorbidities was not a determinant for cardiac monitoring. Of the variance in the adequacy of cardiac monitoring, 15.3% was attributable to physician factors and 5.2% to measured patient factors. Conclusion A large proportion of patients had suboptimal cardiac monitoring. Physician characteristics had more influence than measured patient-level factors in the adequacy of cardiac monitoring. Because trastuzumab-related cardiotoxicity is reversible, efforts to improve the adequacy of cardiac monitoring are needed, particularly in vulnerable populations.