Enlarge ImageImpervious. A mutation in the NQO1 enzyme makes breast cancer cells harder to treat and more likely to spread.Credit: NCI Breast cancer patients with a mutation in both copies of the NQO1 gene have a 20% lower survival rate 5 years after treatment than do patients without the mutation, according to a new study of more than 2000 Finnish women. Those with the mutation were also four times less likely to respond to a common type of chemotherapy. NQO1 encodes an enzyme that protects cells from oxidative stress, damage to the cell and its DNA caused by reactive...