FRIDAY, July 6, 2012 — Scientists have long known that certain breast factors like density and asymmetry are associated with increased risk of breast cancer. How breast size fits into a woman’s odds of developing the disease has been elusive.
Researchers looked at data from more than 16,000 females of European ancestry, who were customers of the genetic-testing company 23andMe, based in California. The women had completed surveys listing bra size, age, genetic ancestry, and personal health history.
“Some studies have found that larger breast size as a young woman is associated with a slightly higher risk for breast cancer," said the study's lead author Nicholas Eriksson, Ph.D., in a report published online in BMC Medical Genetics. "The genetic factors we found support this concept that breast size and breast cancer are related.”
Using this self-reported information — a hallmark of the company’s research — the scientists were able to identify seven gene variations, or single-nucleotide polymorphisms (SNPs), associated with breast growth and size. Two of the seven variations had been previously implicated in developing breast cancer. In each case, the SNP is linked to both increased breast size and increased cancer risk. A third variation is related to breast density and cancer risk.
More Questions Than Answers About Breast Size and Cancer
Two previous studies suggest a correlation between breast size and cancer risk, the authors note. In one, published in the International Journal of Cancer, Harvard researchers found that lean women with a bra cup size of D or larger had nearly twice the risk of cancer as lean women with a bra cup size of A or smaller.
The problem with this conclusion is that it doesn’t offer any insight into what underlying genetic factors, if any, are responsible for the link between size and risk. Until now, very little was known about the DNA behind women’s breast size, except that it’s about 56 percent inherited. This study fills in some of the gaps.
Eriksson did not go so far as to confirm the hypothesis of the Harvard study — that larger breasts equal greater risk — but he did say that the data indicated an interaction between breast morphology and breast cancer risk. He further stressed that more work was needed to determine what his team’s discoveries signify in the big picture of breast cancer risk factors. In the meantime, well-endowed women need not panic; Eriksson says the 23andMe study shows only an association, not causation.
“While the precise relationships between breast size, density, obesity, and breast cancer remain difficult to untangle," Eriksson explained, "understanding the biology behind these developmental processes may be important in understanding breast cancer and may aid in the development of novel screening tools.”