Healthy cells use DNA methylation to switch genes on and off, but in cancer cells this can lead to resistance to treatment, based on research published in The New England Journal of Medicine. The researchers studied colorectal cancer tumors from 220 people, and linked DNA methylation of a gene called TFAP2E to resistance to 5-fluorouracil (5-FU), a drug first discovered in the 1950s. According to the team, this was one of the first studies to link a methylation-based biomarker with chemotherapy resistance. Many cancer chemotherapies are toxic, and biomarkers like this one, that can help physicians to pick out the patients that won't respond, could reduce the number of people that have to endure unpleasant side effects to no clinical advantage. Press release | Abstract