Can mammography screening explain the race difference in stage at diagnosis of breast cancer?

A race difference in the stage at diagnosis of breast cancer is well established: African American women are less likely than white women to be diagnosed at a localized stage. The purpose of this study was to determine the extent to which the observed race (black/white) difference in stage at diagnosis of breast cancer could be accounted for by race differences in the mammography screening history.

This was a population-based, retrospective study of 145 African American and 177 white women with newly diagnosed breast cancer in Connecticut, between January, 1987 and March, 1989. Cases were ascertained through active surveillance of 22 Connecticut hospitals.

Black women were diagnosed more commonly with later stage cancer (TNM stage > or = II) (age-adjusted odds ratio [OR] = 2.01, 95% confidence interval [CI] 1.24-3.24) than were white women. Blacks were also more likely than whites to report that they had not received a mammogram in the 3 years before development of symptoms or diagnosis (OR = 2.05, 95% CI 1.26-3.35); this association was not altered substantially with adjustment for socioeconomic status. In race-specific analyses, mammography was protective against later stage diagnosis in white women, but not in black women. With adjustment for mammography screening, the OR for the race-stage association was reduced only minimally, and race remained a significant predictor of stage at diagnosis.

In these population-based data, history of mammography screening was not an important explanatory variable in the race-stage association. Specifically, history of mammographic screening accounted for less than 10% of the observed black/white difference in stage at diagnosis of breast cancer.