Cell-free DNA methylation tests

Cancer cells carry characteristic DNA methylation patterns that survive in the cell-free DNA shed into blood. Methylation-based tests use bisulfite or enzymatic conversion followed by targeted sequencing to detect a cancer signal and predict its tissue of origin; the multi-cancer early detection test Galleri works this way, and Guardant's Shield, the first blood test approved by the FDA for colorectal cancer screening in 2024, combines methylation with other cfDNA signals. Methylation also underpins some minimal residual disease assays.