Who, When, and How: Watchful Waiting in the ERSPC Rotterdam.

Background and objective: Long-term data identifying which patients managed with watchful waiting (WW) ultimately require androgen deprivation therapy (ADT) are limited. Using 18-yr follow-up data from the Rotterdam section of the European Randomized Study for Prostate Cancer, we examined WW practices and identified prognostic factors for ADT initiation. Methods: Men whose initial management strategy was WW were included and stratified by European Association of Urology risk group. WW practices were evaluated by the frequency of follow-up visits, prostate-specific antigen (PSA) testing, and imaging. Prognostic factors for ADT initiation were identified using a Fine-Gray competing risk model and used to predict 18-yr ADT-free survival for three hypothetical patients representing the risk groups. Key findings and limitations: We included 537 men with a median follow-up of 12.9 yr (interquartile range: 7.5-16.7). At 18 yr, cumulative incidence of ADT initiation was 6.6% (95% confidence interval [CI]: 0.02-13), 33% (95% CI 26-39), and 55% (95% CI 47-64) in men at low, intermediate, and high risk, respectively. Most patients received regular follow-up every 6 mo, regardless of risk group, whereas imaging was uncommon except in men at higher risk. PSA, grade group, and clinical T-stage were statistically significant predictors of ADT initiation. Predicted 18-yr ADT-free survival ranged from 90% in men at low risk to 35% in men at high risk. Limitations include the retrospective design, use of ADT initiation as an end point without standardized triggers, and a historical cohort, possibly affecting internal validity and generalizability. Conclusions and clinical implications: Follow-up for men managed with WW could be individualized based on patient and tumor characteristics to reduce unnecessary visits while preserving timely detection of progression.