Two drinks a day might increase breast cancer risk

Two or more alcoholic drinks a day can increase a woman’s chances of having a specific kind of breast cancer — a type that accounts for roughly 70 percent of all breast cancer — new research shows.

In this so-called hormone receptor–positive breast cancer, a significant number of malignant cells have receptor proteins to which estrogen or progesterone can bind. That binding sends a growth signal into the cell. Indeed, the hormones — particularly estrogen — seem to fuel the cancer.

In the new study, Jasmine Lew and her colleagues at the National Cancer Institute in Bethesda, Md., analyzed questionnaire data collected starting in 1995 from nearly 200,000 postmenopausal women. Over a seven-year period, the scientists obtained detailed biological information on 2,391 women who had cancer and compared this group with women who didn’t have cancer.

Alcohol consumption of two drinks a day increased a woman’s risk of developing hormone receptor–positive breast cancer by 32 percent over nondrinkers’ risk. Having three or more drinks a day increases the risk of such cancer by 51 percent over the teetotalers’ risk.

But the data didn’t show these differences for other breast cancers.

Lew presented the data on April 13 in San Diego at a meeting of the American Association for Cancer Research. She notes that the study is the largest yet to investigate subtypes of breast cancer vis-à-vis alcohol consumption.

Enzymes break down alcohol in the body. Past research suggests that some metabolites, or breakdown products, of alcohol are carcinogenic, says Elizabeth Platz, an epidemiologist at Johns Hopkins University in Baltimore.

“The fact that the association is stronger for estrogen- and progesterone-positive breast cancer lends support to the hypothesis that alcohol influences breast cancer potentially by an estrogenic effect,” she says. In other words, these metabolites may activate some of the same biochemical reactions that estrogen does. That research is still ongoing, Platz says.

Hormone receptor–positive breast cancers are often treatable with anti-estrogen therapy, such as tamoxifen, which blocks estrogen from binding with the receptor. Other drugs work against these cancers by interfering with hormone production.

Weighing risks

Meanwhile, these and other findings have hardened the link between alcohol and breast cancer, raising difficult questions for women.

A benefit to alcohol use became clear in the 1990s when researchers found that people who consumed light amounts of alcohol, one or two glasses a day, were less likely to have heart attacks or strokes than nondrinkers. Alcohol seems to increase HDL, the good cholesterol. More recently, researchers found that light alcohol consumption may make the blood less likely to clot (SN: 11/12/05, p. 317), which could explain part of the protective effect.

But cancer is another story. Two to four alcoholic drinks a day can worsen an existing cancer, a study in mice showed (SN: 4/15/06, p. 238). A long list of other hazards — cancer and otherwise — has historically tainted alcohol use.

Platz says alcohol’s benefits and detriments leave women with difficult choices. A woman with a family history of breast cancer might carry a cancer risk profile with regard to alcohol that is different from that of a woman with no family history, she says. “Such a woman would have to think about ways to modify her cardiovascular disease risk.” Specifically, the woman might use heart-healthy strategies other than drinking, Platz says.