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Breast Cancer Risk Tied to When Smoking Starts 

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. . .

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.

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