We tested 6 CGIs that are frequently aberrantly methylated in clinical colorectal tumours (Supplementary Fig. 1a) and methylated in HCT116 cells (CDKN2A, SFRP1, ZFP42, GATA4, EPHB1, CDH7 and CDH13), a housekeeping CGI promoter that does not become hypermethylated in colorectal cancer, BUB1, and a normally methylated CGI, DAZL (Supplementary Fig. 1a). This evidence concerns the gene SFRP1 and colorectal cancer.