Purpose: To assess long-term cause-specific mortality in breast cancer patients.
Patients and methods: We studied mortality in 7425 patients treated for early breast cancer between 1970 and 1986. Follow-up was 94% complete until January 2000. Treatment-specific mortality was evaluated by calculating standardized mortality ratios (SMRs) based on comparison with general population rates and by using Cox proportional hazards regression.
Results: After a median follow-up of 13.8 years, 4160 deaths were observed, of which 76% were due to breast cancer. Second malignancies showed a slightly increased SMR of 1.2 (95% confidence interval [CI], 1.0-1.3). Radiotherapy (RT) as compared with surgery was associated with a 1.7-fold (95% CI, 1.2-2.5) increased mortality from cardiovascular disease (CVD). After postlumpectomy RT, no increased mortality from CVD was observed (hazard ratio, 1.0; 95% CI, 0.5-1.9). Postmastectomy RT administered before 1979 and between 1979 and 1986 was associated with a 2-fold (95% CI, 1.2-3.4) and 1.5-fold (95% CI, 0.9-2.7) increase, respectively. Patients treated before age 45 experienced a higher SMR (2.0) for both solid tumors (95% CI, 1.6-2.7) and CVD (95% CI, 1.3-3.1).
Conclusion: Currently, a large population of breast cancer survivors is at increased risk of death from CVDs and second cancers, especially when treated with RT at a young age. Patients irradiated after 1979 experience low (postmastectomy RT) or no (postlumpectomy RT) excess mortality from CVD.