Lifestyle factors do not influence genetic risk for breast cancer
MedWire News: Lifestyle risk factors such as the use of hormone replacement therapy (HRT), and age at birth of first child, do not alter the risk for breast cancer associated with low-penetrance susceptibility polymorphisms, study findings indicate.
Recent studies have identified several common single nucleotide polymorphisms (SNPs) that carry a small increased risk for breast cancer. Little is known about how the effects of these genes relate to established lifestyle and behavioral risk factors, collectively referred to as environmental factors, for breast cancer, say Ruth Travis (University of Oxford, UK) and colleagues from the Million Women Study.
To examine this question, Travis and team tested gene–environment interactions in 7610 women with breast cancer and 10,196 women without the disease. They studied the effects of 12 SNPs in relation to 10 established environmental risk factors for breast cancer: age at puberty onset; number of births; age at first birth; breastfeeding; menopausal status; age at menopause; use of HRT; body mass index; height, and alcohol consumption.
After allowance for multiple testing, the researchers found that none of the 120 comparisons (12 SNPS x 10 risk factors) yielded significant evidence of gene–environment interactions.
In particular, and contrary to previous suggestions, use HRT did not affect the risk associated with these common genes, either overall or for estrogen receptor-positive disease.
Although there was no convincing evidence for gene–environment interactions, Travis et al did find that carriers of the high-risk C allele of MAP3K1-rs889312 were significantly shorter than non-carriers (mean height 162.4 vs 163.1 cm).
Travis says: "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."
In an accompanying comment, Steven Narod from the Women's College Research Institute in Toronto, Ontario, Canada, said: "The challenge of breast cancer prevention remains and new approaches are needed."
The study findings are reported in The Lancet.
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By Laura Dean