Comorbidity and survival of Danish breast cancer patients from 2000–2011: a population-based cohort study

Anne Gulbech Ording,¹ Deirdre P Cronin-Fenton,¹ Jacob Bonde Jacobsen,¹ Mette Nørgaard,¹ Reimar Wernich Thomsen,¹ Peer Christiansen,² Mette Søgaard<sup>1

1</sup>Department of Clinical Epidemiology, ²Breast and Endocrine Section, Department of Surgery P, Aarhus University Hospital, Aarhus, Denmark

Objective: Previous studies have suggested that breast cancer survival in Denmark has improved, primarily in cancer patients without comorbidity. We therefore conducted a population-based cohort study to examine recent temporal changes in survival and mortality among breast cancer patients with different extents of comorbidity.
Methods: We used population-based medical and administrative registries to identify breast cancer patients diagnosed between 2000 and 2011 in the Central Denmark Region. We defined comorbid diseases according to the Charlson Comorbidity Index (CCI), including a history of hospitalization for comorbid disease up to 10 years before breast cancer diagnosis. We studied the impact of comorbidities on overall 1- and 5-year survival in different calendar time periods, using a hybrid analysis for survival prediction in the most recent calendar periods.
Results: We included 9,329 breast cancer patients. The proportion of patients within different comorbidity categories remained stable from 2000 to 2011. One-year survival improved from 91% in 2000–2002 to 95% in 2009–2011, while 5-year survival improved from 72% to a predicted 78%. During the entire study period, comorbidity was a strong predictor of the survival of breast cancer patients. However, we observed improvements over time in 1- and 5-year survival for all comorbidity groups. During the 12-year study period, the estimated 5-year survival for patients with a high comorbidity disease burden (CCI score ≥3) increased from 25% to a predicted 50%, and their 5-year age-adjusted mortality hazard ratio (HR) fell from 4.0 (95% confidence interval [CI]: 3.0, 5.4) to 2.7 (95% CI: 2.0, 3.6), respectively, compared with patients with no comorbid disease.
Conclusion: Survival of breast cancer patients diagnosed in the Central Denmark Region improved from 2000 to 2011, regardless of the extent of comorbid disease.

Keywords: breast neoplasm, survival, mortality, comorbidity, prognosis