October 3, 2002 - Young women who start smoking within five years of their first menstrual period face a 70 percent higher risk of developing breast cancer than those who never smoke, a new study has found. This important finding is being reported in the Lancet this week.
The research was based on a study of 2,047 women in British Columbia, with 1018 of them having the disease.
"Our findings have public health consequences, and provide guidance for designing future studies that investigate the relationship between environmental exposures and breast cancer," says principal investigator Dr. Pierre Band of Health Canada. Dr. Band headed the Epidemiology Division of the BC Cancer Agency while the study was conducted.
The higher risk for young female smokers, researchers suspect, is because during puberty, the cells that make up the breast are still forming, and are therefore more susceptible to cancer causing substances. The tissues of a woman's breast don't become fully differentiated until the end of a first and full-term pregnancy.
"The evidence of a detrimental effect of cigarette smoking on this common cancer site reinforces the importance of smoking prevention, particularly in young teens," explains Dr. Nhu Le, a researcher at the BC Cancer Agency, and a co-investigator of the study.
And while cigarette smoke increases the risk of breast cancer among pre-menopausal women, it appears to decrease the risk for some overweight, post-menopausal women.
The possible reason that smoking might inhibit breast cancer in post-menopausal women, says Dr. Le, is that the chemicals in tobacco may block the production of estrogen, which has been linked to breast cancer. The decrease in breast cancer risk was evident among post-menopausal women who began smoking after their first full-term pregnancy, and had gained weight since early adulthood.
Although the study shows that smoking actually decreases the risk of breast cancer in a small group of post-menopausal women, added Dr. Band, it is not advisable to take up smoking as a preventive measure because of the well-established risks of lung cancer and heart diseases.
The BC Cancer Agency, a part of the Provincial Health Services Authority, is committed to reducing the incidence of cancer, reducing the mortality from cancer, and improving the quality of life of those living with cancer. It provides a comprehensive cancer control program for the people of British Columbia by working with community partners to deliver a range of oncology services, including prevention, early detection, diagnosis and treatment, research, education, supportive care, rehabilitation and palliative care. The BC Cancer Research Centre conducts research into the causes and cures for cancer.
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