Temporal trends in breast cancer survival by race and ethnicity: A population-based cohort study

Differences in breast cancer survival by race and ethnicity are often assumed to be a fairly recent phenomenon, and are hypothesized to have arisen due to gaps in receipt of screening or therapy. The emergence of these differences in calendar time have implications for identification of their origin. We sought to determine whether breast cancer survival differences by race or ethnicity arose in tandem with the advent of screening or therapeutic advances.

A cohort of women diagnosed with invasive breast cancer from 1975-2009 in 18 population-based registries were followed for five-year breast cancer cause-specific survival. Differences in survival according to race/ethnicity and estrogen receptor status were quantified in Cox proportional hazards models, with estimation of hazard ratios (HR), 95% confidence intervals (CI), and absolute risk differences. For 2010, we also assessed differences in survival by breast cancer subtypes defined by hormone receptor and Her2/neu status.

Among over 930,000 women, initial differences in five-year breast cancer-specific survival by race became apparent among 1975-1979 diagnoses and continued to be evident, with stronger disparities apparent in those of Black vs. White Non-Hispanic (WNH) race and among estrogen-receptor positive vs. negative disease. Within breast cancer subtype, all included race/ethnic groups experienced disparate survival in comparison with WNH women for triple-negative disease. Black women had a consistent gap in absolute survival of .10-.12, compared with WNH women, from 1975-1979 through all included time periods, such that 5- year survival of Black women diagnosed in 2005-09 lagged more than 20 years behind that of WNH women.

Survival differed by race for diagnoses that predate the introduction of mammographic screening and most therapeutic advances. Absolute differences in survival by race and ethnicity have remained almost constant over 40 years of observation, suggesting early origins for some contributors.