No association between obesity, BRCA mortality among black women

More black women than white women die of invasive breast cancer, but obesity isn’t the reason, a new study from City of Hope (Duarte, California) shows. Because black women tend to be heavier than white women, obesity has been proposed as an explanation for their lower 5-year survival (78% compared with 90% of white women).

To evaluate the effect of obesity on mortality from invasive breast cancer, researchers studied data collected for an earlier breast cancer study on 4,538 women between the ages of 35 and 64 years (1,604 black, 2,934 white) who were diagnosed with invasive breast cancer between 1994 and 1998. They examined the effect of body mass index (BMI) 5 years before diagnosis on death from any cause and death from breast cancer. During a median of 8.6 years of follow-up, 412 black women (25%) died of breast cancer compared with 416 white women (14%). Obese white women (BMI of 30 or higher) had a greater risk of all-cause mortality and breast-cancer-specific mortality than women with a BMI of 20 to 24.9. The association didn’t hold true for black women.

“Obesity may play an important role in mortality among white but not black patients with breast cancer,” the authors write. “It is unlikely that differences in obesity distributions between black women and white women account for the poorer survival of black women.”

Obese white women were 46% more likely to die of breast cancer than white women with a normal BMI, after adjusting for other diseases and education. Black women didn’t show a similar association between obesity and mortality, although the study results suggested a possible link in black women with advanced cancer.

Researchers have speculated that variations in access to health care or tumor biology may affect differences in mortality between black women and white women. Previous studies have shown that black women are more likely than white women to receive a breast cancer diagnosis at a later stage of disease and wait longer to begin chemotherapy after surgery.

The study was published online July 25 in the Journal of Clinical Oncology.