A Targeted Methylation-Based Multicancer Early Detection Blood Test Preferentially Detects High-Grade Prostate Cancer While Minimizing Overdiagnosis of Indolent Disease.

Purpose: Indolent prostate cancer (PCa) is prevalent in the intended use population (adults age 50-79 years) for blood-based multicancer early detection (MCED) tests. We examined the detectability of PCa by a clinically validated, targeted methylation-based MCED test.

Methods: Detectability by Gleason grade group (GG), clinical stage, association of detection status with tumor methylated fraction (TMeF), and overall survival (OS) were assessed in substudy 3 of Circulating Cell-Free Genome Atlas (CCGA; ClinicalTrials.gov identifier: NCT02889978) and PATHFINDER (ClinicalTrials.gov identifier: NCT04241796) studies.

Results: Test sensitivity for PCa in substudy 3 of CCGA was 11.2% (47/420). The test detected 0 (0%) of 58 low-grade (GG1), 3 (1.9%) of 157 favorable intermediate-grade (GG2), 4 (5.1%) of 78 unfavorable intermediate-grade (GG3), and 36 (31.9%) of 113 high-grade (GG4 and 5) cancers and 3 (3.2%) of 95 stage I, 11 (4.7%) of 235 stage II, 7 (14.9%) of 47 stage III, and 22 (81.5%) of 27 stage IV cases. The median TMeF was higher for detected than nondetected cases (2,106.0 parts per million [PPM]; IQR, 349.8-24,376.3 v 24.4 PPM; IQR, 17.8-38.5; P < .05). Nondetected cases had better OS (P < .05; hazard ratio [HR], 0.263 [95% CI, 0.104 to 0.533]) and detected cases had similar survival (P = .2; HR, 0.672 [95% CI, 0.323 to 1.21]) compared with SEER adjusted for age, GG, and stage. Performance was similar in PATHFINDER, with no detected GG1/2 (0/13) or stage I/II (0/16) cases.

Conclusion: This MCED test preferentially detects high-grade, clinically significant PCa. Use in population-based screening programs in addition to standard-of-care screening is unlikely to exacerbate overdiagnosis of indolent PCa.