Relative mortality rates from incident chronic diseases among breast cancer survivors - A 14 year follow-up of five-year survivors diagnosed in Denmark between 1994 and 2007

Background It remains unknown whether incident chronic diseases are more often fatal among breast cancer survivors than among women free of breast cancer. Methods We conducted a nationwide matched cohort study of all Danish breast cancer patients diagnosed between 1994 and 2007, who survived for five years. We compared their long-term mortality with five times as many women from the general population without breast cancer, matched on age. We used time-varying methods to compute mortality rate ratios (MRRs) for incident diseases included in the Charlson Comorbidity Index (CCI). Results One third of five-year breast cancer survivors developed incident diseases during 14 years of follow-up, with about the same incidence as women without breast cancer. Mortality associated with any incident disease was similar among breast cancer survivors (MRR = 7.1, 95% confidence interval (CI): 6.7, 7.4) and comparison women (MRR = 7.5, 95% CI: 7.3, 7.7). Among breast cancer patients, relative mortality associated with incident diseases was higher among patients treated with chemotherapy (MRR = 10, 95% CI: 8.7, 12) and radiotherapy (MRR = 9.8, 95% CI: 8.8, 11) than among patients who received surgery (MRR = 7.0, 95% CI: 6.7, 7.4) or hormonal therapy (MRR = 6.3, 95% CI: 5.8, 6.9). Conclusion There were no marked differences in mortality of diseases among breast cancer survivors and women from the general population. Among breast cancer patients, new diseases were more often fatal in patients treated with chemotherapy and radiotherapy. Five-year breast cancer survivors have similar risk of dying from new chronic medical conditions as women from the general population without breast cancer.