Race, body mass, and stage of breast cancer at diagnosis

Abstract

Background. Black women with breast cancer are more likely to be diagnosed at a later stage compared to white women, which, in part, has been traditionally attributed to social/cultural factors. Black/white differences in the prevalence of obesity have been documented. In most studies, obesity is associated with a later stage of breast cancer 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. Newly diagnosed breast cancer cases (white, N = 585; black, N = 381) were identified from hospitals in the Baltimore metropolitan area from 1991-1997. Patient information including age, race, weight, height, and pathology reports were obtained from hospital medical records. Census-based socioeconomic status (SES, including income and education) were obtained from 1990 U.S. Census files. Results. Black women were more likely than white women to be diagnosed with breast cancer at TNM stage II or greater (age-adjusted odds ration (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 (age-adjusted OR = 2.70; 95% CI, 2.01-3.61). A high body mass was significantly associated with an advanced stage of breast cancer at diagnosis (OR 1.59; 95% CI, 1.17-2.16). This association was more apparent in young women (<50 years, OR = 2.47; 95% CI, 1.43-4.28) than in older women (OR = 1.30; 95% CI, 0.90-1.90). Adjustment for the higher prevalence of obesity in black women reduced the risk of later stage of breast cancer at diagnosis in black women compared to white women by approximately 30%. Conclusions. Obesity is a risk factor for later stage of breast cancer at diagnosis, particularly in young women. The higher prevalence of obesity among young black women may play 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 and SES.