The Validity of a New Procedure-Based Definition of Cancer Status in Patients with Breast-, Lung- and Colorectal Cancer in the Danish National Patient Registry.

Background/Aim: The Danish National Patient Registry (DNPR) provides unique epidemiological insight, but often lacks granular data. We propose a procedure-based definition of cancer status in patients with breast-, lung- and colorectal cancer, which can be applied to administrative health databases. New definitions of cancer status are needed as mortality and morbidity are closely linked to cancer status, yet most studies only use duration since cancer diagnosis as a severity marker. The aim of the study was to validate a new pragmatic definition. Methods: Medical journals of 600 patients, with breast-, lung- and colorectal cancer from the Department of Oncology at Herlev-Gentofte Hospital were retrospectively reviewed. We defined active cancer as a cancer diagnosis, not followed by a potentially curative procedure within 6 months of the diagnosis. The remaining patients were characterized as having non-active cancer. This dichotomization was then compared to a cancer status assessment based on treatment received and paraclinical test such as their first post-procedural control scan. Based on this comparison, we calculated the positive predictive value (PPV) of our definitions of active and non-active cancer. Results: The calculated PPVs for active breast-, lung- and colorectal cancer were 87% (CI 95%: 0.74-0.99), 91% (CI 95%: 0.87-0.96) and 82% (CI 95%: 0.73-0.91). The PPVs for non-active breast-, lung- and colorectal cancer were 95% (CI 95%: 0.92-0.99), 91% (CI 95%: 0.82-0.99) and 73% (CI 95%: 0.66-0.81), respectively. Conclusion: We found an overall high PPV for both active and non-active cancer across all three types of cancer.