Validating clinical assumptions for characterizing prostate cancer aggressiveness utilizing historical cancer registry data.

The prognosis of prostate cancer is highly dependent on disease characteristics at diagnosis, and dilution effects can compromise etiological studies that are not stratified by disease aggressiveness. However, such classifications are often hindered by missing staging data. This study aimed to develop and validate clinical assumptions to consolidate information about clinical TNM stage and Gleason score (GS) for improved classification of aggressive and non-aggressive disease. A total of 17 551 males diagnosed with prostate cancer (1974-2022) in the Norwegian Janus Serum Bank cohort were included. The developed clinical assumptions were validated using positive predictive values (PPVs) among males with non-missing data and long-term cancer-specific mortality. Cases were classified as aggressive (cT4, N1, M1, or GS ≥ 8) or non-aggressive (complete information without aggressive features) with and without applying the clinical assumptions. Of the 14 developed clinical assumptions, 8 had a PPV > 95%. Applying these assumptions nearly halved the proportion of cases with unclassifiable aggressivity (from 59% to 32%). Fifteen-year cumulative mortality [95%CI] was higher for previously unclassifiable cases newly classified as aggressive (53.4% [47.6-59.7]) than for cases originally classified as aggressive (42.6% [40.5-44.8]). Clinical assumptions to consolidate TNM and GS information can substantially improve the classification of aggressive and non-aggressive prostate cancer.