The socioeconomic gradient in all-cause mortality for women with breast cancer: Findings from the 1998 to 2006 National Cancer Data Base with follow-up through 2011

Purpose: To analyze the association between socioeconomic status (SES) and all-cause mortality among women diagnosed with breast cancer before and after controlling for insurance status, race and ethnicity, stage, treatment modalities, and other demographic and hospital characteristics. Methods: Data analyzed included follow-up through 2011 for 582,396 patients diagnosed between 1998 and 2006 with ductal carcinoma in situ or invasive (stage I-IV) breast cancer from the National Cancer Data Base. SES was measured by grouping patients into six income and education-level ZIP code categories. Hierarchical Cox regression models were used to analyze SES survival differences. Results: Five- and 10-year survival probabilities for the highest SES group were 87.8% and 71.5%, versus 79.5% and 61.5% for the lowest SES group. Controlling for all covariates reduced the highest-to-lowest SES hazard ratio from 1.69 (95% confidence interval: 1.64-1.74) to 1.27 (95% confidence interval: 1.24-1.31). Results were virtually identical in models that included comorbidity and invasive cancer patients only. Conclusions: Differences in insurance status, race, and stage at diagnosis are important components of SES disparities and explain about two-thirds of the initial SES survival disparity. The residual SES effect likely mirrors underlying social determinants of health for all American women.