The increased risk of breast cancer associated with a range of common genes is not affected by lifestyle factors including use of hormone replacement therapy, age at birth of first child, obesity and alcohol consumption, according to Ruth Travis, DPhil of the Cancer Epidemiology Unit, University of Oxford, UK, and colleagues from the Million Women Study.
Recent studies have identified several common genetic variations which carry a small increased risk of breast cancer. Little is known about how the effects of these genes relate to the established lifestyle and behavioral risk factors for breast cancer. The authors have examined this question in detail for the first time in a large UK study of women’s health, according to a press release.
The study included 7,160 women who developed breast cancer and 10,196 women without breast cancer, who each provided a blood sample for genetic testing as well as information on lifestyle factors. The authors studied the risk of breast cancer for 12 genetic variants in the women’s DNA, in relation to 10 established environmental risk factors — age at puberty onset, number of births, age at first birth, breastfeeding, menopausal status, age at menopause, use of hormone replacement therapy, body-mass index, height, and alcohol consumption.
None of the 120 comparisons yielded significant evidence of gene-environment interactions. In particular, and contrary to previous suggestions, use of hormone replacement therapy did not affect the risk associated with these common genes.
This lack of interaction means that although both genetic and environmental factors separately increase breast cancer risk, they appear to do so independently. This study did not include the well-known, much rarer breast cancer susceptibility genes such as BRCA1 and BRCA2. These carry a high risk of breast cancer but affect relatively few women.
“Known risk factors for breast cancer include both lifestyle factors and inherited genetic factors. We looked at whether lifestyle factors for breast cancer, such as use of HRT, alcohol consumption and reproductive history, influence the genetic risks: and the answer is that they do not.”