DNMT1 and DNMT3B mutations or amplifications are more common in cancers of epithelial tissues of the breast, ovaries, skin, bladder, lung and colon (reviewed in Zhang et al., 2020), whereas loss-of-function DNMT3A mutations are the most frequent lesions identified in acute myeloid leukemia (AML) where they are found on average in 30% of patients (Ley et al., 2010; Cancer Genome Atlas Research, 2013; Brunetti et al., 2017). The gene discussed is DNMT1; the disease is cancer.