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Breast Cancer Risk Tied to When Smoking Starts

Danger higher when habit begins within 5 years of first period

THURSDAY, Oct. 3, 2002 (HealthDayNews) -- Canadian researchers say that a young woman who smokes can increase the risk that she will have breast cancer decades later.

But the researchers also find that cigarette smoking appears to decrease the breast cancer risk for some older women. The research appears in the Oct. 5 issue of The Lancet.

Those apparently conflicting effects stem from the interaction among the carcinogens in cigarette smoke, breast cells and estrogen, the female sex hormone, says Pierre R. Band, lead author of the report. He did the study while head of epidemiology at the British Columbia Health Agency and now is senior medical epidemiologist at Health Canada, that nation's equivalent of the U.S. Department of Health and Human Services.

Breast tissue is most sensitive to the cancer-causing effect of carcinogens around the time of puberty, when its cells have not fully developed and are dividing rapidly, Band says. But in older women, those who have gone through menopause, smoking reduces the estrogen activity that can stimulate growth of cancer cells.

Childbearing and body weight also enter the equation, the report says. The study finds that for premenopausal women, the risk is increased for those who start to smoke within five years of the onset of menstruation and who later become pregnant, because smoking does not offset the surge of estrogen activity in those years. On the other hand, postmenopausal women whose body mass index, an indication of obesity, had increased since age 18 and who started to smoke after they had a baby had a significantly decreased risk of breast cancer.

If all of this sounds complicated to you, Dr. Irma Russo, chief of molecular endocrinology at the Fox Chase Cancer Center, agrees. "I've spent 30 years trying to figure it out," says Russo, who wrote an accompanying editorial.

But one basic message does emerge, Band and Russo say. "The public health message is that our observations reinforce the importance of smoking prevention, especially in early adolescence," Band says. "Women who start smoking at puberty, at 10 or 15 years of age, might be diagnosed with breast cancer at 40," Russo says.

The results come from a survey that compared 1,431 women with breast cancer in British Columbia and 1,502 women without breast cancer. One result that jumped out was that women who had not yet gone into menopause and who started smoking within five years of the onset of menstruation had a 70 percent higher risk of breast cancer than nonsmokers. By contrast, the risk of breast cancer for postmenopausal women who started to smoke after a first pregnancy was only half that of nonsmokers.

Those results suggest strategies for studying different aspects of the breast cancer problem, Band says. One focus of research should be the "window of susceptibility" to cancer-causing agents, he says. Women who start smoking early in life should be the target population for studies looking at the effects of cancer-causing agents, while the effects of hormones, and the drugs that influence their action, should be studied in women who have gone through menopause.

"Not every woman who smokes will develop breast cancer, just as not every man who smokes will develop lung cancer," Russo says. "So we must identify the populations that are at risk. We need to identify those populations and focus our attention on them."

What To Do

Learn more about the risk factors for breast cancer from the National Cancer Institute. Meanwhile, the Centers for Disease Control and Prevention has plenty of information on the ills of smoking and some help if you want to quit.

SOURCES: Pierre R. Band, Ph.D, senior medical epidemiologist, Health Canada, Quebec; Irma Russo, M.D., chief of molecular epidemiology, Fox Chase Cancer Center, Philadelphia; Oct. 5, 2002, The Lancet
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