Jim Crow and estrogen-receptor-negative breast cancer: US-born black and white non-Hispanic women, 1992-2012.

PURPOSE: It is unknown whether Jim Crow-i.e., legal racial discrimination practiced by 21 US states and the District of Columbia and outlawed by the US Civil Rights Act in 1964-affects US cancer outcomes. We hypothesized that Jim Crow birthplace would be associated with higher risk of estrogen-receptor-negative (ER-) breast tumors among US black, but not white, women and also a higher black versus white risk for ER- tumors.
METHODS: We analyzed data from the SEER 13 registry group (excluding Alaska) for 47,157 US-born black non-Hispanic and 348,514 US-born white non-Hispanic women, aged 25-84 inclusive, diagnosed with primary invasive breast cancer between 1 January 1992 and 31 December 2012.
RESULTS: Jim Crow birthplace was associated with increased odds of ER- breast cancer only among the black, not white women, with the effect strongest for women born before 1965. Among black women, the odds ratio (OR) for an ER- tumor, comparing women born in a Jim Crow versus not Jim Crow state, equaled 1.09 (95% confidence interval [CI] 1.06, 1.13), on par with the OR comparing women in the worst versus best census tract socioeconomic quintiles (1.15; 95% CI 1.07, 1.23). The black versus white OR for ER- was higher among women born in Jim Crow versus non-Jim Crow states (1.41 [95% CI 1.13, 1.46] vs. 1.27 [95% CI 1.24, 1.31]).
CONCLUSIONS: The unique Jim Crow effect for US black women for breast cancer ER status underscores why analysis of racial/ethnic inequities must be historically contextualized.