For the subgroup of patients who had surgical tissue assayed, there was no difference in methylation in tumour tissue between the 56 ctDNA-positive and 35 ctDNA-negative cases at peri-diagnosis (median (IQR): BCAT1, 43.4% (27.1–59.2) and 52.6% (26.1–68.2), respectively, P = 0.533; IKZF1, 59.3% (20.5–84.4) and 59.0% (16.6–100.3), respectively, P = 0.430). Here, BCAT1 is linked to neoplasm.