Does stage at diagnosis influence the observed relationship between socioeconomic status and breast cancer incidence, case-fatality, and mortality?

Historically, lower socioeconomic status (SES) has been reported to be associated with decreased breast cancer incidence and mortality and increased case-fatality, although recent trends in breast cancer screening and treatment may alter these relationships. This study assessed the associations between SES and breast cancer incidence, case-fatality, and mortality by stage of disease at diagnosis using recent data in the United States. Breast cancer incidence and survival data from the Surveillance, Epidemiology, and End Results (SEER) tumor registry for black and white women aged 55 and above were linked to county level SES and population data based on place of residence. Poisson regression was used to calculate age-adjusted relative rates associated with SES levels and breast cancer incidence, case-fatality, and mortality. As SES decreased, localized breast cancer incidence rates decreased, while incidence rates of distant disease increased. Five-year localized and regional breast cancer case-fatality rates increased as SES decreased. Localized breast cancer mortality rates decreased as SES declined, whereas regional breast cancer mortality rates tended to increase. These results confirm some previously reported findings and suggest that associations between lower SES and lower localized breast cancer mortality rates are influenced mainly by underlying associations between SES and localized breast cancer incidence, whereas regional breast cancer mortality rates appear to reflect the underlying association between SES and regional case-fatality rates.