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The Premenopausal Breast Cancer Collaborative Group undertook an international prospective study to determine the links between BMI and breast cancer risk.
Although a higher body mass index (BMI), a measure of body fat composition, is associated with an increased risk of many kinds of cancer, it is unusual in its relationship to breast cancer. Unlike other cancers, which are linked to similar cancer risks across the lifespan, high BMI can decrease the risk of breast cancer before menopause, and increase it afterwards.
In a new study published in JAMA Oncology by The Premenopausal Breast Cancer Collaborative Group, researchers investigated the links between BMI and breast cancer in women between the ages of 18 and 54.
The researchers used self-reported questionnaire data from 758,592 North American, European, Asian, and Australian women from 19 prospective studies. This included a total of 13,082 breast cancer cases. The researchers then analyzed the participants by age category and breast cancer type.
The researchers found that BMI was negatively associated with breast cancer, meaning that the higher the BMI, the lower the risk. However, underweight women appeared to have about the same risk as normal weight women, and the protective effect diminished with age.
In situ (non-invasive) cancer was more strongly associated with BMI at ages 25-44, hormone receptor-negative breast cancer was correlated with BMI at 18-25 years of age, and hormone receptor-positive breast cancer was also strongly correlated with BMI at all ages. Importantly, women with higher BMI also were more likely to have received a mammogram.
The differences in breast cancer risk at different BMIs may be linked to childhood weight and the speed of puberty and the adolescent growth spurt in children, which are both tightly linked to hormones like estrogen in women. They may also be linked to the tissue composition of the breast itself, as different tissue densities in breasts are also linked to different breast cancer risks.
Further work will need to focus on clarifying the mechanisms by which BMI is linked to breast cancer risk, and whether the association is a matter of overall body fat, hormone levels, or other factors.
Written by C.I. Villamil
Reference: Schoemaker M, Nichols H, Wright L, Brook M, Jones M, O’Brien K et al. Association of Body Mass Index and Age With Subsequent Breast Cancer Risk in Premenopausal Women. JAMA Oncology. 2018.