Smoking and breast cancer risk in Denmark

The effect of smoking on breast cancer risk was evaluated in a population-based case-control study, including 1,480 women diagnosed with breast cancer in Denmark between 1983–84. They were identified from the files of the nationwide clinical trial of the Danish Breast Cancer Cooperative Group and the Danish Cancer Registry. The control group was an age-stratified sample of 1,332 women from the general population. Data on risk factors were collected by self-administered questionnaires. The risk of breast cancer among current smokers and ex-smokers was similar to that in non-smokers, both risk estimates being close to unity. No dose-response relation was observed for any measure of smoking (age at start, duration, number of cigarettes per day, or cigarette-years of exposure) in all subjects, and when pre- and post-menopausal women were examined separately. These findings suggest that smoking is not associated with the risk of breast cancer.This work was undertaken during tenures of fellowships awarded to Dr. M. Ewertz by the Danish Cancer Society and the International Agency for Research on Cancer. The study was funded by the Danish Cancer Society, the Danish Medical Research Council, and Astrid Thaysens Legat.Dr Ewertz is with the Danish Cancer Registry, Institute of Cancer Epidemiology, Danish Cancer Society, Rosenvaengets Hovedvej 35, Box 839 DK-2100 Copenhagen Ø, Denmark.