Environmental factors do not heighten the genetic risks of breast cancer

Women who inherit genes linked to breast cancer have no greater risk than other women of developing the disease as a result of lifestyle choices, including hormone replacement therapy (HRT) and alcohol consumption, according to a recent study in The Lancet.

In the first large scale study to consider the additive effects of genetic make-up and lifestyle, scientists investigated the interaction between nature and nurture in 7610 women who developed breast cancer and 10,196 healthy controls. The researchers looked at 12 common gene polymorphisms associated with breast cancer and ten known lifestyle risk factors (age at menarche, parity, age at first birth, breastfeeding, menopausal status, age at menopause, use of hormone replacement therapy, body-mass index, height, and alcohol consumption).

Of the 120 possible independent gene-environment permutations examined none supported a significant increase in breast cancer risk, so whilst both genetic and environmental factors separately increase breast cancer risk, they appear to do so independently. The researchers concluded: 'There was no convincing evidence for gene-environment interaction'.

'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' said Ruth Travis, lead researcher of the study conducted at University of Oxford.

'Genes account for only a small proportion of breast cancers for most women and for most women the main risk remains the lifestyle factors... the good news is that some of these are modifiable, so by changing their behaviour women can alter their risk of breast cancer', said Jane Green, a co-author of the study.

'This study provides another piece in the jigsaw, helping us to understand how genes and lifestyle affect breast cancer risk,' she added.

The study did not, however, cover data on the BRCA1 and BRCA2 genes, which have a far stronger association to breast cancer than the other genetic variants assessed, but are less commonly found in the population.