Socioeconomic Status and Survival after an invasive Breast Cancer Diagnosis

Abstract

Abstract Significant progress has been achieved in the United States in improving survival rates following an invasive breast cancer diagnosis. Previous studies have shown, however, that women living in geographic areas with high poverty and low education levels experience poorer survival. However, nearly all of these studies have been restricted to use of community-level data (e.g. US Census) on socioeconomic status (SES), and thus have been limited in their ability to identify individual-level factors associated with the disparity in survival. We examined individual-level SES in relation to breast cancer survival in a population-based cohort of invasive breast cancer survivors, ages 20-69, diagnosed in Wisconsin during 1995-2003 (N = 5,865). Information on household income, household size, and education was obtained during telephone interviews conducted shortly after diagnosis. Vital status was determined through December 31, 2006, using automated searches of the National Death Index. A total of 676 deaths (461 from breast cancer) were observed during 41,751 person-years of follow-up. Compared to college graduates, women with no further education beyond high school were more likely to die from breast cancer (Hazard Ratio, HR: 1.39; 95% CI: 1.10, 1.76) and from all causes (HR 1.42; 95% CI: 1.17, 1.73) following their breast cancer diagnosis. Similarly, women with household income less than 2.5 times that of the poverty level were more likely to die from breast cancer (HR 1.46; 95% CI: 1.03, 2.08) and from all causes (HR 1.64; 95% CI: 1.20, 2.24) compared to women with household income at least 5 times the poverty level. Women with lower education and income levels were less likely to have had annual mammograms prior to diagnosis. There was little difference in stage at diagnosis according to education level, but women with low income levels were 2.7 (95% CI: 1.2, 6.2) times more likely than women with high income to be diagnosed with distant-stage breast cancer. Adjustment for these factors attenuated, but did not eliminate, the association between SES and survival after diagnosis. Thus, the disparities in breast cancer survival that exist according to individual-level SES cannot be fully explained by variation in mammography use and stage at diagnosis.