Covariance of breast cancer incidence with smoking-, oestrogen- and diet-related cancers in pre- and postmenopausal women in Sweden

Effects of smoking on breast cancer risk remains controversial. Tar products have been claimed to increase risk, antioestrogenic effects to reduce risk. Another possibility is that associations to smoking have been confounded by diet. The increasing incidence of breast cancer from 1960 to 1994 in Sweden is parallel to that of lung cancer and the increasing proportion of female smokers. The incidence of endometrial and colon cancer was in premenopausal women negatively and in postmenopausal women positively related to the incidence of breast cancer. Possible explanations and hypotheses to the different co-variance between breast cancer and lung, endometrial and colon cancer in pre- and postmenopausal women are discussed from the perspectives of smoking, sex hormones and diet. it is concluded that the strong and specific positive relationship between breast and lung cancer in premenopausal women is compatible with the hypothesis that aromatic hydrocarbons may be involved in the causation of disease.