Absence of an anticipated racial disparity in interval breast cancer within a large health care organization.

Purpose: Compared to non-Latina (nL) white women, nL black women are diagnosed with more aggressive breast cancers, which in turn should be more likely to go undetected on screening mammography and subsequently arise as interval breast cancer (IBC). We sought to estimate the extent of an anticipated racial disparity in IBC within a single, large health care organization.

Methods: The present analysis focuses on 4357 breast cancers diagnosed between 2001 and 2012 and within 18 months of a screening mammogram (N = 714,218). We used logistic regression with model-based standardization (predictive margins) to estimate adjusted prevalence differences corresponding to a racial disparity in IBC.

Results: Overall, prevalence of IBC within 18 months was 20.7%. Contrary to expectation, in patient-adjusted models, there was no IBC racial disparity (percentage point disparity = -2.1, 95% confidence interval: -4.7, 2.6). However, when controlling for facility characteristics, including proportion of nL black patients, the model coefficient for the IBC disparity reversed sign and changed substantially (P < .0001) and a racial disparity emerged (percentage point disparity = +5.1, 95% confidence interval: -0.3, 9.9).

Conclusions: The sorting of patients by race across facilities appears to have mitigated an otherwise anticipated disparity in IBC. Possible explanations are discussed.