Comparison of Relative Survival and Cause-specific Survival in Men with Prostate Cancer According to Age and Risk Category. Nationwide, Population-based Study.

Net survival, estimated in a relative survival (RS) or cause-specific survival (CSS) framework, is a key measure of the effectiveness of cancer management. We compared RS and CSS in men with prostate cancer (PCa) according to age and risk category, using Prostate Cancer data Base Sweden, including 168 793 men below age 90 diagnosed 1998-2016 with PCa. RS and CSS were compared according to age and risk category based on TNM stage, Gleason, and PSA. Each framework requires assumptions that are unlikely to be appropriate for PCa. Ten-year RS was substantially higher than CSS in men age 80-89 with low-risk PCa, 125% (95% CI 113-138%) vs 85% (95% CI 82-88%). In contrast, RS and CSS were similar for men below age 70 and for all men with regional or distant metastases. Both RS and CSS produce biased estimates of net survival for men with low and intermediate-risk PCa, in particular for men above 80. Due to biases, net survival is overestimated in analysis of RS but underestimated in analysis of CSS. These results highlight the importance of evaluating the underlying assumptions for each method, as the 'true' net survival is expected to lie between the limits of RS and CSS.