Premenopausal women who carry excess fat around their abdomen or have a large waist relative to their hip size may face a higher risk for breast cancer that is estrogen receptor (ER)-negative, new research reveals.The research team noted that such body fat distribution was linked more strongly to the risk for developing this particular type of cancer than it was to a risk for ER-positive breast cancer.Body fat distribution of this kind was not associated with an increased risk for breast cancer generally, according to the study, published Dec. 15 in the Journal of the National Cancer Institute.Estrogen receptor (ER)-negative breast cancer means that the cancer lacks receptors for the female hormone estrogen, so the hormone does not stimulate the cancer to grow.The research team, led by Holly R. Harris of Brigham and Women's Hospital and Harvard Medical School in Boston, pointed out that prior research had suggested that body fat composition (as indicated by body mass index, or BMI) has a complex relationship with cancer risk.For example, having a higher BMI has previously been linked to a rise in the risk for postmenopausal breast cancer, but not premenopausal breast cancer.On the other hand, the researchers said that premenopausal women who carry excess fat that wraps around organs in the abdominal region are more likely to develop the pre-diabetic condition known as hyperinsulinemia. Lab experiments have shown that insulin receptors can promote the growth of breast cancer cells.In their latest investigation, Harris and her colleagues focused on data from more than 116,000 women who had been enrolled in the Nurses’ Health Study II since 1989, including waist and hip circumference, recorded in 1993.The fact that ER-negative breast cancer was more strongly linked to abdominal fat and the waist-hip ratio than ER-positive breast cancer suggests, according to the researchers, that the means by which body fat distribution influences cancer risk sidesteps sex-hormone pathways.The findings "may suggest that an insulin-related pathway" related to abdominal fat is involved in the development of premenopausal breast cancer, the authors wrote.Source: ivillage.com