Tahhan, Sami

LBA10509 Background: The MCED test (Galleri) detects a shared cancer signal from cell-free DNA in blood and predicts a cancer signal origin (CSO) to guide diagnostic (dx) workup. PF2 (NCT05155605) is a large, prospective, multicenter, interventional study of the MCED test’s performance and safety in a diverse US intended-use population. Methods: PF2 enrolled participants aged ≥50y without clinical suspicion of cancer or cancer diagnosis/treatment within 3y of enrollment. Primary objectives were MCED performance and safety in terms of dx testing triggered by a positive (cancer signal detected) MCED test result. Participants with a positive MCED test underwent targeted dx workup guided by the predicted CSO(s). Participant-reported anxiety was assessed with the State Trait Anxiety Inventory. Results: PF2 enrolled 35,878 participants; 32,007 with a 12m cancer assessment were analyzable for performance. Of 287 (0.9%) with a positive MCED test, 173 were diagnosed with cancer within 12m, for a cancer detection rate of 0.5% (95% CI 0.5-0.6%) and positive predictive value of 60.3% (54.5-65.8%). Specificity was 99.6% (99.6-99.7%). 12m episode sensitivity was 69.8% (62.8-76.0%) in a prespecified subgroup of 12 cancers responsible for ⅔ of US cancer deaths, 66.2% (55.1-75.8%) in a subgroup of 6 aggressive cancers with low 5y survival, and 39.3% (34.9-44.0%) across all cancers. Overall CSO prediction accuracy was 91.3% (86.2-94.7%) across all cancers. The MCED test detected 151 new primary and 22 recurrent cancers; additional cancers detected by screening were those with USPSTF A/B (n=31) and C (n=60) recommended screening. Of 151 MCED-detected new primaries, 80 (53.0%) were clinical stage I-II; 107 (70.9%) were stage I-III. Of 80 MCED-detected stage I-II cancers, 71.2% had no USPSTF A/B screening recommendation. Of 35,335 participants analyzable for safety, 213 (0.6%) had invasive procedure(s) to evaluate a positive MCED test result, of which 90% were nonsurgical and 1.8x more likely for participants with vs without cancer diagnosis. Most (87.6%) had a CSO-guided dx evaluation. There were 5 study-related adverse events during the time of dx workup; none were serious. Anxiety temporarily increased for participants with a positive MCED test and cancer diagnosed, and returned to baseline by 12m. Of participants with a positive MCED test, median time from test result to dx resolution was 48d (95% CI 43-56). Few participants (7/63 [11.1%]) had cancer found by dx PET/CT after a targeted dx workup that did not reveal cancer. Conclusion: The MCED test demonstrated robust performance with a favorable safety profile. When MCED testing was added to USPSTF A/B screening, 6.5x more cancers were detected by screening, most at early stages. The diverse, representative PF2 participant population supports the generalizability of these findings to the US intended-use population. Clinical trial information: NCT05155605 .

Abstract A blood-based multi-cancer early detection (MCED) test has demonstrated feasibility as a screening tool in large-scale clinical trials. The PATHFINDER 2 (PF2) study (NCT05155605) evaluates safety and performance of the MCED test in a diverse intended-use population. To gauge generalizability of study results, we assessed participant (ppt) baseline characteristics vs general US population data from the National Health and Nutrition Examination Survey (NHANES). PF2, a prospective, multicenter, interventional study, enrolled ppts aged ≥50 y from diverse clinical settings in North America. Enrollment targets for sex and race/ethnicity were established from the 2019 American Community Survey (US Census Bureau). Recruitment strategies were implemented to maximize enrollment for groups historically underrepresented in clinical studies. Exclusion criteria included clinical suspicion of cancer or cancer diagnosis/treatment within 3 y. Data on baseline characteristics and key cancer risk factors were collected at enrollment. We compared the PF2 study population to a nationally representative sample of US adults aged ≥50 y from 2017-2020 NHANES data. NHANES data were weighted using complex, multistage probability sampling to generate a nationally representative sample. There were 35,878 ppts enrolled in PF2; 35,307 clinically eligible and evaluable ppts were included in this analysis. Mean age was 64 y for both PF2 and NHANES; 56.2% were females in PF2 vs 53.6% (95% CI 52.0-55.3%) in NHANES. Race/ethnicity distribution for PF2 vs NHANES was 7.4 vs 11.0% (8.9-13.1%) Hispanic, 74.6 vs 69.7% (65.0-74.5%) non-Hispanic (NH) White, 8.6 vs 10.3% (7.6-13.1%) NH Black, and 5.8 vs 5.1% (3.5-6.8%) NH Asian. In terms of lifestyle characteristics for PF2 vs NHANES, 58.9 vs 29.2% (25.8-32.7%) had at least a bachelor’s degree, 74.8 vs 63.8% (60.6-67.0%) were married/living with a partner, 69.3 vs 53.8% (50.9-56.7%) had never smoked, 66.5 vs 70.4% (68.0-72.8%) were overweight/obese, and 24.2 vs 28.4% (26.4-30.3%) reported never using alcohol. PF2 enrolled a diverse ppt population that is reasonably reflective of the demographics of the US population aged ≥50 y. As is typical for clinical trials, a higher percentage of PF2 vs NHANES ppts reported lifestyle characteristics associated with better health. As the study population largely reflects the MCED test intended-use population, safety and performance results from PF2 are expected to reflect real-world clinical experience. Citation Format: Shirish Gadgeel, Nima Nabavizadeh, Dax Kurbegov, Charles McDonnell, III, James W. Lillard, Jr., Marc Matrana, Alan Roth, Andrea Johnston, Sami Tahhan, Rami Owera, Matthew Margolis, Anuraag Kansal, Margarita Lopatin, Margaret McCusker, Karthik V. Giridhar. Baseline participant characteristics from PATHFINDER 2, a prospective interventional study of a multi-cancer early detection test in a population setting [abstract]. In: Proceedings of the 18th AACR Conference on the Science of Cancer Health Disparities; 2025 Sep 18-21; Baltimore, MD. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2025;34(9 Suppl):Abstract nr C145.