Background: Lung cancer is the leading cause of cancer-related death in Denmark. Since 2001, the Danish Lung Cancer Registry (DLCR) has monitored interventions and outcome of all Danish lung cancer patients with the intent to streamline and improve treatment and survival over time. The DLCR receives information from the Danish Patient Registries complimented with clinical information from the treating physicians. DLCR is used extensively for research on lung cancer in Denmark. This study evaluates the validity of the information in the DLCR.

Methods: Patients diagnosed with non-small cell lung cancer from 2014 to 2016 and recorded in the DLCR were included, and a random sample of 1000 patients were selected for validation. Medical records (electronic files) were reviewed and were considered as the ?gold standard? to which data listed in the DLCR were compared.

Results: So far information has been retrieved in the medical charts for 834 patients. Agreement of stage at diagnosis was 86.3% (CI 83.8-88.5), excluding missing stage in charts 91.2% (CI 89.8-94.8). Agreement of treatment intent were 92.8% (CI 90.2-94.0) and date of diagnosis (± 6 months) were 804/834 (96.4%). Agreement of smoking status in pack years (± 5 pack years) were 450/518 (86.9%) (smoking information missing for 316 patients) and WHO performance status was 69.7% (CI 66.1-73.1).

Conclusion: The comparison of data from the DLCR with the medical records revealed high validity of the data in the registry. The results of this study are similar to validation of other clinical Danish cancer registries and the DLCR is considered useful for research purposes.