The common C677T polymorphism in the MTHFR gene results in a considerably lower enzyme activity [46] that probably increases intracellular folate concentrations, making tumors exhibiting mutated MTHFR genotypes more sensitive to cytotoxicity than wild-type MTHFR tumors [48], if there are no differences in MTHFR genotype between tumor and somatic cells of the patient. The gene discussed is MTHFR; the disease is neoplasm.