Smoking and Breast Cancer

Ex-smokers are exposed to a higher breast cancer risk than are never smokers. This conclusion is based on a follow-up of the 10 902 women in the Malmö Preventive Project. The 31% higher incidence in ex-smokers remained statistically significant when other risk factors were taken into account in the analysis. In both smokers and ex-smokers there was an increased incidence of oestrogen receptor negative tumours. In ex-smokers, but not in smokers, there was similarly an overrepresentation of poorly differentiated tumours.

Many women who give up smoking gain weight and obesity may be associated with increased lipid levels in the blood. Breast cancer incidence in ex-smokers was higher in women with high serum levels of triglycerides, but not in women with high cholesterol.

Probability of survival following breast cancer is only partly related to stage at diagnosis. In a follow-up of 792 breast cancer patients within the Malmö Mammographic Screening Trial, it was shown that, stage by stage, smokers had a less favourable prognosis than never smokers.

Breast cancer mortality rates differ substantially between residential areas in Malmö. In an analysis of incident cases and deaths between 1986-96, it was shown that stage at diagnosis, rather than incidence, contributes to this pattern. Areas with a high proportion of advanced carcinomas, and a high case-fatality rate, had a higher prevalence of smokers, ex-smokers, foreigners and residents receiving income support.

It is concluded that smoking is a risk factor for breast cancer and that smoking contributes to the pattern of breast cancer mortality.