Can obesity explain the racial difference in stage of breast cancer at diagnosis between black and white women?

Objective: Black women are more likely to be diagnosed at a more advanced stage of breast cancer than are white women. Traditionally, this has been attributed in part to social or cultural factors. Given that black women are more likely to be obese than white women and that being obese is associated with a more advanced stage at diagnosis, this study aims to assess to what extent the racial difference in stage at diagnosis can be explained by racial differences in obesity.

Methods: Incident cases of breast cancer between 1991 and 1997 (white, n = 585; black, n = 381) were identified from hospitals in the Baltimore metropolitan area. Information, including age, race, weight, height, and pathology reports, was obtained from hospital medical records.

Results: Black women were more likely than white women to be diagnosed with breast cancer at tumor-node-metastasis (TNM) stage II or greater (age-adjusted odds ratio [OR] = 1.51, 95% confidence interval [CI] 1.15-1.99). Further, black women were more likely than white women to be overweight or obese. A high body mass index (BMI) was significantly associated with an advanced stage of breast cancer at diagnosis. Adjustment for the higher prevalence of obesity in black women attenuated the risk estimate of more advanced stage of breast cancer at diagnosis in black women compared with white women by approximately 30%.

Conclusions: Our results suggest that the higher prevalence of obesity among black women plays an important role in explaining their relative disadvantage in stage at diagnosis of breast cancer. Nonetheless, a racial difference in stage of breast cancer at diagnosis persists after adjustment for obesity.