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We all know that smoking causes lung cancer. The link between smoking and other types of cancer is less well recognized, but also important. Joanna Karpasea-Jones reported on this site that smoking before menopause raises the risk of breast cancer. Smoking after menopause also raises the risk of breast cancer, according to a study by Dr. Juhua Luo of West Virginia University and colleagues at eight research institutions across the country.
Luo's study included 79,990 women aged 50 – 79 selected from the Women's Health Initiative Observational Study. Women with a history of cancer, other than non-melanoma breast cancer, were excluded. The average follow-up period was 10.3 years, during which time 3,520 cases of invasive breast cancer were identified.
Breast cancer rates for this group were 16 percent higher in current smokers and 9 percent higher in former smokers, compared to women who never smoked. The highest breast cancer rates were found in women who smoked for more than 50 years. In former smokers, the risk declined with time since quitting smoking. It took up to 20 years for the former smokers' risk to return to the baseline level of women who never smoked.
The risk of passive smoking was less conclusive, since it is difficult to find subjects over age 50 who have not been exposed to passive smoke. Luo concluded, “the association with passive smoking should be considered suggestive only and needs confirmation from other studies.”
In addition to smoking, Luo found other factors associated with breast cancer in this group:
1. Non-Hispanic white ethnicity
2. Higher education
3. No pregnancies or higher age at first pregnancy
4. History of taking estrogen plus progesterone hormone therapy
5. Heavier alcohol intake
6. Family history of breast cancer
Similar results on the link between smoking and breast cancer were found by Dr. Ourania Kosti and colleagues at Georgetown University Medical Center, Washington, D.C. These researchers concluded that sensitivity to mutagens in tobacco smoke is an important risk factor for both pre- and post-menopausal women.