Performance evaluation of a reflex blood-based methylated ctDNA multi-cancer early detection test in individuals with obesity.

100 Background: Obesity increases risk of 13 distinct cancers, most without screening programs, and collectively representing 40% of all annual US cancer diagnoses.With recent CDC data (2023) showing that obesity rates exceed 35% in 23 U.S. states, multi-cancer early detection (MCED) testing represents a unique opportunity to address a critical screening gap in this population. In this case-control study, we examined the performance of a reflex blood-based ctDNA methylation MCED test in individuals with obesity (BMI ≥ 30 kg/m 2 ), evaluating cancer-specific intrinsic accuracy (sensitivity) and positive predictive value (PPV). Methods: We analyzed peripheral blood samples (NCT05435066) from individuals with obesity, including 424 treatment-naïve cancer patients and 458 non-cancer controls, using a reflex test by Harbinger Health. The test system consists of a primary methylome profiling test optimized for high sensitivity (rule-out), followed by a confirmatory reflex analysis utilizing an expanded methylation panel designed to achieve high PPV (rule-in) and tissue of origin (TOO) classification. Test performance metrics were derived using 10-fold cross-validation with patient-level stratification. Overall cancer incidence in the obese population was estimated at 1.6%. Prospective PPV for each TOO readout was calculated using cancer-specific intrinsic accuracy estimated from the case-control study in combination with incidence values. Results: In this cohort (mean age 57.1 ± 13.4 years; 63.3% female; 67.8% White; 22.4%, Black or African American), the test achieved an overall 29.7% (95CI, 25.3-34.6) correct-TOO sensitivity (66.1% false negative, 4.2% incorrect TOO) at 98.9% (95CI, 97.6-99.6) specificity and 98.9% negative predictive value (95CI, 98.85,99.0). Among a subset of cancers associated with obesity, TOO-specific PPVs were: hepatobiliary (HB: liver, biliary duct; 100%; 95CI, ND), CRC (87.5; 95CI, 61.1-96.9), upper gastrointestinal (UGI; 81.8; CI95, 48.6-95.5), uterine (66.7%; 95CI, 26.5-91.7), pancreaticobiliary (PB: pancreas, gallbladder; 17.6%; 95CI 3.1-59.0). Corresponding cancer group sensitivities (early stage, I-II) were: HB 50.0 (35.1), CRC 51.9 (28.6), UGI 40.9 (9.1), uterine 8.5 (3.8), PB 56.5 (25.0). In a modeled cohort of 100,000 tested individuals, the expected TOO readout counts (correct case-type odds) were: 23 for HB (23:0), 60 for CRC (7:1), 42 for UGI (9:2), 23 for uterine (2:1), 279 for PB (1:5). Conclusions: Inindividuals with obesity at increased risk for multiple cancers, especially those lacking established screening guidelines, the reflex ctDNA methylation MCED test demonstrated clinically meaningful PPV and early-stage sensitivity for each cancer type. These results warrant prospective validation to assess the test’s clinical validity and utility in early-stage cancer detection in this high-risk population.