Blood-based tests for multicancer early detection (PATHFINDER): a prospective cohort study

Background: Multi-cancer early detection (MCED) blood tests can detect a cancer signal from circulating cell-free DNA (cfDNA). PATHFINDER was a prospective cohort study evaluating the feasibility of MCED testing for cancer screening. Methods: Between December 2019 and December 2020, a convenience sample of 6662 adults ≥50 years without signs or symptoms of cancer consented to MCED testing. Blood was collected, cfDNA analyzed, and results returned to participants’ physicians. If a cancer signal was detected, predicted cancer signal origins (CSOs) informed diagnostic evaluation. The primary outcome was time to, and extent of, diagnostic testing required to confirm the presence or absence of cancer. Findings: Cancer signal was detected in 92 (1.4%) of 6621 participants with analyzable results. There were 35/92 true positive (TP) and 57/92 false positive (FP) results. Excluding two participants whose diagnostic evaluations began before MCED test results were reported, median time to diagnostic resolution was 79 days (IQR 37–219): 57 (33–143) in TP and 162 (44–248) in FP participants. Most had both laboratory tests (26/33, 79% TP; 50/57, 88% FP) and imaging (30/33, 91% TP; 53/57, 93% FP). Fewer procedures were performed in FP (17/57, 30%) than TP (27/33, 82%) and few had surgery (one in FP; three in TP). Interpretation: This study supports the feasibility of MCED screening for cancer and underscores the need for further research evaluating its clinical utility.