Does comorbidity interact with prostate cancer to increase mortality? A Danish cohort study of 45 326 prostate cancer patients diagnosed during 1995–2011

Abstract

Background: Many prostate cancer patients die of other causes, but it remains unknown whether comorbidity interacts synergistically with prostate cancer to increase the mortality rate beyond that explained by the individual risks of comorbidity and prostate cancer.

Methods: A nationwide cohort study of 45 326 Danish prostate cancer patients diagnosed during 1995–2011, each matched to approximately five men from the general population on age and individual comorbidities in the Charlson Comorbidity Index (CCI). We calculated five-year mortality rates and interaction contrasts as a measure of the excess mortality rate explained by synergy between prostate cancer and comorbidity.

Results: Five-year mortality was 46.8% in prostate cancer patients and 25.8% in matched men from the general population. For prostate cancer patients with a CCI score of 2–3, the mortality rate was 250 per 1000 person-years [95% confidence interval (CI): 236, 263], and interaction between comorbidity and prostate cancer accounted for 20% of the total mortality rate (50 deaths per 1000 person-years, 95% CI 35, 65) in the first year following cancer diagnosis. The interaction was mainly present for patients with metastatic disease and those not treated with prostatectomy.

Conclusion: Up to 20% of all deaths among men who had both prostate cancer and comorbidities could be explained by the comorbidity-prostate cancer interaction. The mortality attributable to comorbidity itself and the mortality attributable to the interaction may be reduced by successful treatment of the comorbidity.