While it's was known that breast size is in part heritable, the study is the first to find specific genetic factors that are associated with differences in breast size, the researchers said. In addition, two of these markers have previously been associated with breast cancer risk
. This suggests some of the same biological pathways underlie both normal breast growth and breast cancer, said study researcher Nicholas Eriksson, of 23andMe, the genetic testing company that conducted the study.
The study alone does not provide enough evidence to link breast size to breast cancer. But it may contribute to a better understanding of the role that breast structure plays in breast cancer risk, the researchers said.
In the study, Eriksson and colleagues analyzed information from 16,175 female customers of European ancestry, and compared their answers to survey questions, including bra cup size and bra band size, to their genetic information.
While breast density is known to be a risk factor for breast cancer
, the effect of breast size is less clear. A few previous studies have found that larger breast size is associated with an increased risk of breast cancer in lean women.
The new study was published online June 30 in the journal BMC Medical Genetics.