Lead author Christopher I. Li, M.D., Ph.D., and colleagues reported their findings in the October issue of Cancer Epidemiology, Biomarkers and Prevention.
Higher Risk of Breast Cancer
"Women who were current drinkers who reported consuming at least 30 grams of alcohol a day - roughly the equivalent of two drinks - had an 80 percent higher risk of breast cancer compared to nondrinkers," said Li, an assistant member of Fred Hutchinson's Public Health Sciences Division.The risk varied by cellular, or histologic, breast-cancer type. "Current consumers of two or more drinks per day had more than three times the risk of lobular cancer (a 330 percent increased risk) and a 50 percent increased risk of ductal cancer," Li said.
Rise in Lobular Breast Cancer
While lobular breast cancer, which involves the lobules, or chambers in the breast that contain milk-producing glands, accounts for only 10 percent to 15 percent of all breast-cancer cases, its incidence is on the rise. Li and colleagues earlier this year reported a 65 percent increase in lobular cancer during the past decade, a trend that may be due to the increased use of combined estrogen and progestin hormone-replacement therapy, Li said (Journal of the American Medical Association, March 19, 2003).Ductal breast cancer, which involves the ducts that carry milk from the lobules to the nipple, accounts for about 80 percent of cases. The incidence of this form of breast cancer has remained essentially constant during the past decade.
Risk Is Hormonal Based
While somewhat more difficult to diagnose than ductal breast cancers, lobular carcinomas tend to be ER+ and PR+, which means they are more responsive to hormonal therapies such as tamoxifen that block the tumor-promoting effects of estrogen. Li and colleagues observed that current users of alcohol had a 40 percent increased risk of ER+/PR+ breast cancers."The marked increase in hormonally sensitive breast cancers, including lobular and ER+/PR+ tumors, among women who drink suggests a hormonal basis for the known association between alcohol use and breast-cancer incidence," Li said. "Alcohol is known to increase estrogen levels in the blood, and therefore it could stimulate hormonally sensitive tumors."
Cancer More Difficult to Treat
The researchers found no association between alcohol use and increased incidence of hormonally insensitive cancers (estrogen-receptor negative and progesterone-receptor negative, or ER-/PR-, tumors). Since these types of tumors can grow independent of estrogen and progesterone, they are unresponsive to hormonal blockers such as tamoxifen and therefore are more difficult to treat.
Different Types of Breast Cancer
While alcohol use has been associated with a moderate increase in breast-cancer risk, few studies, until now, have stratified results by histology (cancer type) or hormone-receptor status, Li said."This is one of the first studies to evaluate the relationship between alcohol use and breast cancer and how alcohol consumption modifies the risk of different types of breast cancer. While our results suggest that alcohol is strongly associated with hormonally responsive types of breast cancer, they need to be confirmed by other researchers," said Li, also a research assistant professor of epidemiology at the University of Washington School of Public Health and Community Medicine.
Nearly 2,000 western Washington women, ages 65 to 79, were interviewed for the study; half had a history of breast cancer and half did not.
