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. The findings are reported in an Article Online First and in an upcoming Lancet , by Dr Ruth Travis 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 behavioural ('environmental') 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.
The study included 7160 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 (single nucleotide polymorphisms, SNPs) 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 (12 SNPs x 10 risk factors) 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.
The study's main author, Dr Ruth 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. "
Co-author Dr Jane Green adds*: "Known risk factors for breast cancer include both lifestyle factors and inherited genetic factors. We looked at whether the effects of recently identified genetic risk factors for breast cancer are modified by known lifestyle risk factors for breast cancer, such as use of HRT and obesity: and the answer is that they are not."
In an accompanying Comment, Dr Steven A Narod, Women's College Research Institute, Toronto, ON, Canada, says: "The challenge of breast cancer prevention remains with us and new approaches are sorely needed."
Cancer Epidemiology Unit, University of Oxford, UK: Dr Ruth Travis: T) +44 1865 289642 E) ruth.travis@ceu.ox.ac.uk ; Dr Jane Green: T) +44 1865 289659 E) jane.green@ceu.ox.ac.uk
University of Oxford Press Office, Jonathan Wood: T)+44 1865 280530 E) jonathan.wood@admin.ox.ac.uk
Dr Steven A Narod, Women's College Research Institute, Toronto, ON, Canada T) +1 416 351 -3765 / +1 416 351-3766 E) Steven.narod@wchospital.ca
For full Article and Comment see: http://press.thelancet.com/breastgenes.pdf
Note to editors: *quotes direct from authors and cannot be found in text of Article
The Lancet