38 Background: FDA approved 3 androgen receptor inhibitors for nonmetastatic castration-resistant prostate cancer (nmCRPC) based on global randomized trials with control arms of placebo + ADT. Despite similar enrolled populations, grade 1 or higher investigator-reported, Common Terminology Criteria for Adverse Events (CTCAE)-graded fatigue ranged 11-25% in the placebo arms. We sought to characterize variability in investigator-reported, CTCAE-graded fatigue across geographic regions and compare this with the variability in patient-reported fatigue. Methods: Data from patients receiving ≥ 1 placebo dose were reviewed from control arms of 3 nmCRPC double-blind, placebo-controlled trials submitted to FDA. We determined worst grade clinician-reported (ClinRO) CTCAE fatigue, and most severe fatigue reported by patient-reported outcome (PRO) for each patient at any time during treatment or within 30 days of last dose in each trial by geographic region: North America/Western Europe (NAWE) versus rest of the world (ROW). We compared variability in fatigue rates to those of a more objective AE, CTCAE-defined anemia. Results: NAWE enrollment comprised 46-75% of placebo cohorts. Median age was comparable across trials and regions. ClinRO CTCAE fatigue was higher in NAWE (15-33%) compared to ROW (8-14%) in each of the 3 placebo cohorts (see Table). Rates of PRO fatigue varied by region (50-73% in NAWE compared to 42-59% in ROW), and the regional differential was present at baseline. Anemia rates were similar in NAWE and ROW in each trial ( < 5%) per CTCAE. Conclusions: CTCAE reporting of fatigue, a subjective symptom, was inconsistent across sites. Anemia, an objective AE, was more consistently reported. ROW investigators less frequently reported fatigue compared to NAWE investigators. Reasons for this are unclear, but could include cultural and language factors. PRO fatigue was relatively consistent across trials and regions. These results should be interpreted with caution, as we acknowledge the limitations of cross-trial comparison.[Table: see text]