Overweight women at risk of aggressive triple-negative breast cancers

Excess weight puts women at risk not only for estrogen-fueled breast cancers but also more aggressive, harder-to-treat triple-negative cancers that lack receptors for estrogen, HER2, and progesterone, a new study from the Fred Hutchinson Cancer Center shows.

The study, published online March 11 in Cancer Epidemiology, Biomarkers and Prevention, examined data from 155,723 women enrolled in the Women’s Health Initiative study of the effects of hormone replacement therapy on menopausal women. Of the women in the WHI study, 307 had triple-negative breast cancer and 2,610 had estrogen receptor-positive (ER+) breast cancers. When researchers analyzed body mass index (BMI) in these women, they found that women with the highest BMI had a 35% higher risk of triple-negative breast cancers and a 39% higher risk of ER+ breast cancers.

In addition, researchers found an association between physical activity and triple-negative breast cancers. Women who reported no recreational physical activity had higher risks of both triple-negative and ER+ breast cancers than women in the highest activity tertile. Waist and hip circumference were positively associated with risk for ER+ but not triple-negative cancers.

“Despite biological and clinical differences, triple-negative and ER+ breast cancers are similarly associated with BMI and physical activity in postmenopausal women” the authors write. “The biological mechanisms underlying these similarities are uncertain and these modest associations require further investigation.”