DNMT1 and cancer: In cancers, 5hmC patterns undergo considerable changes4 that have been linked to genome instability5, 6 and remodelling of the DNA methylation pattern.7 Previous studies revealed that 5hmC is consistently found at significantly reduced levels in various solid tumours.8–10 Indeed, epigenetic regulators such as DNA methyltransferases (DNMT), ten-eleven-translocation (TET) proteins or isocitrate dehydrogenases (IDH), are crucial for normal and malignant cellular developement.11 Very few studies however, have effectively mapped the distribution of 5hmC in normal or cancer tissues.