Impact of Charlson Comorbidity Index conditions on one-year survival in patients with breast cancer: a Danish population-based cohort study

Abstract

Breast cancer is the most frequently diagnosed malignancy in women. The Charlson Comorbidity Index (CCI) is a widely used tool for quantifying multimorbidity. As the population ages, breast cancer incidence and comorbidity prevalence are expected to grow. We therefore investigated the absolute and relative impact of the CCI conditions on 1-year mortality in Danish patients with breast cancer. In this population-based cohort study, we identified women with breast cancer from 1987 to 2022 using the Danish Cancer Registry. We estimated 1-year mortality using the Kaplan–Meier method and adjusted hazard ratios (aHRs) using Cox proportional hazards regression. Analyses were stratified by calendar year, cancer stage, and age at diagnosis. Among 146,397 women with breast cancer (median age: 63.4 years; localized stage: 51%), 27.5% had at least one CCI condition. The most prevalent conditions were chronic pulmonary disease (6.5%), non-metastatic solid tumors (6.0%), and cerebrovascular disease (5.6%). One-year mortality was highest in women with dementia (27.3%), congestive heart failure (21.7%), and metastatic solid tumors (20.4%). All CCI conditions, except connective tissue disease, were associated with elevated mortality. The highest hazard ratios were observed for AIDS (aHR: 4.54 [95% confidence interval (CI): 1.46–14.1]), moderate to severe liver disease (aHR: 3.53 [95% CI: 2.70–4.61]), and metastatic solid tumors (aHR: 2.26 [95% CI: 1.92–2.66]). Mortality declined over time, with an impact of CCI conditions across time periods seen for absolute but not for relative risks. The impact of comorbidities was greater among younger women and those with localized or regional spread cancer. Most CCI conditions were associated with elevated 1-year mortality in Danish patients with breast cancer, although absolute mortality declined substantially over time. Our findings provide updated estimates of the prognostic impact of individual CCI conditions in patients with breast cancer.