Anne Wojcicki, chief executive officer of 23andMe, said the researchers identified seven single-nucleotide polymorphisms significantly associated with breast size, including three single-nucleotide polymorphisms also correlated with breast cancer in a genome-wide association study.
The researchers analyzed data from 16,175 female 23andMe customers of European ancestry and compared their answers to survey questions, including bra cup size and bra band size to genetic data at millions of single-nucleotide polymorphisms.
"The findings in this study show that some of the same biological pathways underlie both normal breast growth and breast cancer," lead author Nicholas Eriksson said in a statement. "Some studies have found that larger breast size as a young woman is associated with a slightly higher risk for breast cancer. The genetic factors we found support this concept that breast size and breast cancer are related."
The findings, published online in BMC Medical Genetics, make the first concrete genetic link between breast size and breast cancer risks, Wojcicki said.
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