Being overweight might increase the risk of triple-negative breast cancers, US researchers said.
It's already known that excess weight increases the risk of oestrogen-receptor positive breast cancers, likely because oestrogen accumulates in the fat and promotes tumours.
The new study showed that overweight women had a 35% higher risk of developing triple-negative breast cancer, which lack the oestrogen, progesterone or HER2 receptors needed for most breast cancer drugs to work.
Triple-negative tumours are found in 10% to 20% of cases.
How the study was done
"The fact that we found an association with triple-negative breast cancer is unique because, biologically, this subtype is very different from other breast cancers," said Dr Amanda Phipps of the Fred Hutchinson Cancer Research Centre in Philadelphia, whose report appeared online in Cancer Epidemiology, Biomarkers & Prevention.
For her study, Dr Phipps and colleagues analysed data from 155,723 women enrolled in the Women's Health Initiative study of the effects of hormone replacement therapy on menopausal women.
The team compared body mass index and physical activity among the 307 women in the study who had triple negative breast cancer and the 2,610 women who had oestrogen receptor-positive breast cancers.
Women in the highest BMI quartile had a 35% higher risk of triple-negative breast cancers, and a 39% higher risk of oestrogen-fed breast cancers, compared to women in the lowest quartile.
Dr Phipps said the effect was modest, but if confirmed by other teams, the study offers women new ways to reduce their risk of triple-negative breast cancers.
(Reuters Health, Julie Steenhuysen, March 2011)