Therefore, if the dose of MTX is higher than 2.5 g/m2, in patients with NK/T cell lymphoma and ANKL, it is necessary to detect the genotype of MTHFR rs1801131 and adjust the dose of MTX or lengthen the duration of leucovorin rescue in patients with the AA genotype, in order to decrease the risk of developing hematopoietic toxicity. This evidence concerns the gene MTHFR and extranodal nasal NK/T cell lymphoma.