In a study of more than 16,000 women, those with larger breasts were found to be more likely to have genetic mutations that are linked to breast cancer.
The researchers have suggested the correlation could be down to the sex hormone oestrogen that can trigger the growth of mammary glands and tumours. The breast size in question was the density, meaning the breast tissue that is not fat.
Researchers read the genetic code of the participating women – all of European origin- and looked through tiny mutations of their DNA.
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Their results showed seven genetic factors significantly associated with breast size - three of which are strongly correlated with mutations already linked to breast cancer.
Dr Eriksson of the California-based genetics firm 23andMe used data volunteered by the women themselves by means of a questionnaire.
Participants were asked to give their bra size on a 10-point scale from smaller than AAA to larger than DDD, the scientists then compared the results with genetic data on millions of mutations.
“Our results identify genetic variants that have an effect on both breast cancer and natural variation in breast size,” said Dr Eriksson.
“Most of the genetic factors we identified for breast size lie in regions of great importance for breast cancer.
He added: “These findings show some of the same biological pathways underlie both normal breast growth and breast cancer.”
Although the research has identified the first substantial link between breast size and cancer, he added much more work was needed before it could be considered concrete.
“This isn’t a huge surprise if you think of cancer as unrestrained growth. But the relationship between breast size and breast cancer is complicated.
“The connections between these genetic factors - breast size and breast cancer aren’t fully understood - our findings give clues to the function of some of these genes and regions that might be useful in combating breast cancer,” Dr Eriksson concluded.
The link was seen regardless of the women’s age, pregnancy and breastfeeding history and genetic ancestry, according to the study published in the journal BMC Medical Genetics.