NEW YORK (Reuters Health) - Smoking is a major risk factor for breast cancer among women with a family history of breast or ovarian cancer, US researchers report.

Their study of 132 families with at least three breast or ovarian cancer patients found that patients' sisters and daughters who smoked were more than twice as likely to develop breast cancer, compared with the nonsmoking sisters and daughters of patients. Smoking did not appear to increase the risk among patients' nieces and granddaughters, however, according to the report published in the April issue of Cancer Epidemiology, Biomarkers & Prevention. In families with the strongest genetic risk--those with at least five members with cancer--smoking was an even more significant risk factor. Patients' sisters and daughters who smoked at some point in their lives were nearly six times more likely to develop breast cancer than relatives who never smoked. ``Breast cancer is not typically thought of as a smoking-associated malignancy but for susceptible women it could be quite an important contributor,'' Dr. Thomas A. Sellers of the Mayo Clinic in Rochester, Minnesota, and the study's senior author, told Reuters Health. The researchers explain that smoking boosts carcinogens, or cancer-causing chemicals, in the blood. These chemicals can cause mutations in the DNA of breast cells which, over time, lead to cancer. The study authors call for further research into the link between cigarette smoking and breast cancer among women with a genetic risk. ``If you don't smoke, don't start. If you do smoke, it's never too late to quit,'' Sellers said. SOURCE: Cancer Epidemiology, Biomarkers & Prevention 2001;10:327-332.

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