Evaluating information loss in the National Cancer Database from cases lost to follow-up

Background and Objectives: Cancer registries must focus on data capture which returns value while reducing resource burden with minimal loss of data. Identifying the optimum length of follow-up data collection for patients with cancer achieves this goal. Methods: A two-step analysis using entropy calculations to assess information gain for each follow-up year, and second-order differences to compare survival outcomes between the defined follow-up periods and lifetime follow-up. A total of 391 567 adult cases, deidentified in the National Cancer Database and diagnosed in 1989. Comparisons examined a subset of 61 908 lung cancer cases, 48 387 colon and rectal cancer cases, and 64 134 breast cancer cases in adults. A total of 4133 pediatric cases were diagnosed in 1989 examining 1065 leukemia cases and 494 lymphoma cases. Results: Annual increases in information gain fell below 1% after 16 years of follow-up for adult cases and 9 years for pediatric cases. Comparison of second-order differences showed 62% of the comparisons were similar between 15 years and lifetime follow-up when examining restricted mean survival time. In addition, 90% of the comparisons were statistically similar when comparing hazard ratios. Conclusions: Survival analysis using 15 years postdiagnosis follow-up showed minimal differences in information gain compared to lifetime follow-up.