The incidence of breast cancer, as well as other chronic disease, increases with age, older breast cancer patients being more likely than younger to suffer from other diseases at time of diagnosis. Our objective was to assess the effect of comorbidity on mortality after early breast cancer. 62,591 women diagnosed with early breast cancer 1990-2008 were identified using the Danish Breast Cancer Cooperative Group Registry. Data were linked to the Danish National Patient Register and the Danish Register of Causes of Death. Main outcome measures were mortality from all causes, breast cancer, and non-breast cancer causes in relation to Charlson comorbidity index (CCI). Compared with patients without comorbidity (CCI 0), the presence of comorbidity increased the risk of dying from breast cancer as well as other causes with adjusted hazard ratios (HRs) for all-cause mortality of 1.45 (CI 95% 1.40-1.51) for CCI 1, 1.52 (95% CI 1.45-1.60) for CCI 2, and 2.21 (95% CI 2.08-2.35) for CCI 3+. Equivalent HRs for breast cancer-specific mortality were 1.30 (95% CI, 1.24-1.36) for CCI 1, 1.31 (95% CI 1.23-1.39) for CCI 2, and 1.79 (95% CI, 1.66-1.93) for CCI 3+ (all P values < 0.0001). For patients with CCI 0, 5-year overall survival increased over time from 72.5% (95% CI, 71.7-73.3%) in 1990-1994 to 81.6% (95% CI, 80.9-82.2) in 2000-2004, whereas the 5-year overall survival remained stable around 43% among the patients with CCI 3+. This population-based cohort study shows that compared with patients without comorbidity, the risk of dying from breast cancer as well as other causes increased significantly with increasing CCI score. While survival improved over time for patients without comorbidity, no improvement was seen among patients with severe comorbidity (CCI 3+).

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Background: While comorbidity indices are useful for describing trends in survival, information on specific comorbidities is needed for the clinician advising the individual breast cancer patient on her treatment. Here we present an analysis of overall survival, breast cancer-specific mortality, and effect of medical adjuvant treatment among breast cancer patients suffering from 12 major comorbidities compared with breast cancer patients without comorbidities. Material and methods: The study population was identified from the Danish Breast Cancer Cooperative Group and included 59,673 women without prior cancer diagnosed with early-stage breast cancer in Denmark from 1990 to 2008 with an estimated median potential follow-up of 14 years and 10 months. Information on comorbidity and causes of death was derived from population-based registries. Multivariable proportional hazards regression models were used to assess the effect of comorbidities on mortality, all-cause and breast cancer specific, using patients without comorbidity as reference. Results: At breast cancer diagnosis, 16% of patients had comorbidities and 84% did not. Compared with the latter, the risk of dying from all causes was significantly increased for all types of comorbidity, but the risk of dying from breast cancer was significantly increased only for peripheral vascular disease, dementia, chronic pulmonary disease, liver, and renal diseases. Comorbidities diagnosed within 5 years of breast cancer diagnosis correlated with a greater risk of dying than comorbidities diagnosed more than 5 years before breast cancer diagnosis. With a few exceptions, the effect of adjuvant treatment on breast cancer mortality was similar among patients with and without comorbidity. Conclusion: Breast cancer mortality was not significantly elevated for patients with prior myocardial infarction, congestive heart failure, cerebrovascular disease, connective tissue disease, ulcer disease, and diabetes. The similar effect of adjuvant treatment in patients with and without comorbidity underlines the importance of adhering to guideline therapy.