So far, two studies have reported that in MTX-resistant cell lines, the promyelocytic leukemia HL-60 cell line (Drummond et al., 1997) and the colon cancer cell line HT-29 (Kim et al., 2021), DHFR and MSH3 were often co-amplified, leading to an overexpression of both genes. Here, MSH3 is linked to acute promyelocytic leukemia.