Comorbidity among Danish lung cancer patients before and after initial cancer diagnosis.

Lung cancer is the leading cause of cancer-related death worldwide. This population-based longitudinal study investigates survival rates and the burden of comorbidity before and after being diagnosed with lung cancer in Denmark. From the Danish National Patient Registry (NPR) and the Danish Civil Registration System (CPR), 53,749 patients with lung cancer were identified and matched with 214,304 controls on age, gender, region of residence and marital status in the period 1998-2010. From the NPR, data on survival and comorbidity, registered as ICD-10 diagnoses, were extracted. Comorbidity was assessed using the Deyo-Charlson comorbidity score (DCcs) and mortality using Kaplan-Meier survival curves. 1-year survival rate for Danish lung cancer patients was 51.7 % (CI 51.3-52.1) and 5-year survival rate was 14.7 % (CI 14.3-15.0) compared to 96.8 % (CI 96.7-96.8) and 84.0 % (CI 83.9-84.2) for controls respectively. Overall, cases had significantly more comorbidity compared to controls before being diagnosed with lung cancer. Prior to being diagnosed with lung cancer, more cases than controls had been diagnosed with other malignancies (11.4 % vs 6.0 % p<0.005), diseases of the circulatory system (16.4 % vs 13.0 % p<0.005) and respiratory diseases (12.2 % vs 4.8 % p<0.005). Among lung cancer patients 21.8 % had a DCcs ≥ 1 compared to 13.3 % among controls (P<0.005). The 1-year survival for DCcs =0 was 54.8 % (CI 54.3-55.3) for lung cancer patients and 97.8 % (CI 97.7-97.9) for controls. Decreasing survival with increasing DCcs was found in both groups. This study provides unique nationwide comorbidity data on patients before and after being diagnosed with lung cancer. We found increased mortality with increasing comorbidity, however more pronounced among controls compared to patients with lung cancer.