Conversely, if the dose of MTX is higher than 2.5 g/m2, in patients with TLBL, ALL and CML-LBC, it is necessary to detect the genotype of MTHFR rs1801133 and adjust the dose of MTX or lengthen the duration of leucovorin rescue in patients with the CT and TT genotypes in order to decrease the risk of developing hematopoietic toxicity. The gene discussed is MTHFR; the disease is chronic myelogenous leukemia, BCR-ABL1 positive.