April 14, 2008 (San Diego) -- Even a drink or two a day of alcohol may raise the risk of the most common type of breast tumors -- those fueled by the hormones estrogen and progesterone, according to one of the largest studies if its kind.
A second study shows that specific variations within two genes involved in metabolizing alcohol are associated with an increased risk for breast cancer in postmenopausal women.
While the studies do not prove cause and effect, they lend plausibility to growing evidence implicating drinking as a risk factor for breast cancer, says Elizabeth Platz, ScD, a specialist in cancer prevention at the Johns Hopkins Bloomberg School of Public Health.
"The beauty of the research is that it tells us something about the mechanisms" by which alcohol may raise breast cancer risks, she tells WebMD.
Platz moderated a news conference to discuss the findings at the annual meeting of the American Association for Cancer Research.
Alcohol and Breast Cancer Risk
Some breast tumors are fueled by hormones, while others are not. In the first study, National Cancer Institute (NCI) researchers wanted to determine if the hormone status of a tumor influences the relationship between alcohol use and breast cancer risk.
The researchers reviewed data on 184,418 postmenopausal women, who answered questions about how much alcohol and what type of alcohol they drank each day. They were followed for an average of seven years.
Overall, moderate drinking raised the risk of developing breast cancer, regardless of whether a woman's preference was for beer, wine, or hard liquor. And the more she drank, the greater the risk.
But most of the increased risk was seen in women whose tumors were fueled by both estrogen and progesterone, says Jasmine Q. Lew, a fourth-year medical student at the University of Chicago who led the research.
These tumors, referred to by doctors as being estrogen-receptor and progesterone-receptor positive, or ER+/PR+, account for many breast cancers.
Compared with teetotalers, women who drank one to two drinks a day were 32% more likely to develop ER+/PR+ breast cancer. Having three or more drinks daily raised the risk of ER+/PR+ tumors by 51%.