Objective: To compare survival of patients with breast cancer who had never smoked, were smokers, and who were ex-smokers.
Design: Observational study.
Setting: City of Malmö, Sweden.
Patients: 792 patients with breast cancer diagnosed between 1977-1986 in the Malmö mammographic screening trial.
Interventions: Follow-up of breast cancer cases through record-linkage with the Swedish Cause of Death Registry.
Main outcome measures: Death from breast cancer. Relative risk (RR) with 95% confidence interval (CI) of death from breast cancer was calculated for different smoking groups using Cox's proportional hazards analysis.
Results: During a mean follow-up of 12.1 years, 145 patients died of breast cancer. Breast cancer mortality was 1347/10(5) person-years in those who had never smoked, 1941/10(5) in smokers, and 1493/10(5) in ex-smokers. The crude RR for smokers and ex-smokers, compared with those who had never smoked were 1.44 (1.01 to 2.06) and 1.13 (0.66 to 1.94), respectively. The RR associated with smoking remained significant after adjustment for age and stage at diagnosis, 2.14 (1.47 to 3.10), and other potential confounders.
Conclusions: Survival after breast cancer was, as expected, strongly related to stage at diagnosis. However, stage by stage there was considerable variation between individual patients. We conclude that differences with regard to exposure to smoking contribute to this heterogeneity.