Black women are three times more likely than other women to develop an aggressive form of breast cancer characterised by "triple negative tumours", a study published Wednesday found.
The findings, published in BioMed Central's open access journal Breast Cancer Research, held true even when other risk factors such as lifestyle, age and weight were taken into account.
In the United States, where the study was conducted, the overall incidence of breast cancer is lower in black women than in white women.
But when black women do get breast cancer, it tends to be more advanced when diagnosed, has a higher risk of recurring, and a less favourable outcome.
Researchers led by Carol Rosenberg of Boston University analysed 415 breast cancer cases and noted the number of "triple negative" tumours, so called because three critical proteins -- estrogen and progesterone receptors, and the HER2 gene -- malfunction.
"The odds of having a triple-negative tumour were three times higher for black women than for non-black women," said Rosenberg in a press statement.
It had been known that pre-menopausal black women were disproportionately affected by this deadly form of cancer, but the new study showed that these tumours were just as common in black women diagnosed before or after age 50, obese or not.
"The higher prevalence of triple negative breast tumours in black women in all age and weight categories likely contributes to black women's unfavourable breast cancer prognosis," Rosenberg said.