近年来 ,由于化疗方案的不断改进 ,小儿急性淋巴细胞白血病 (ALL)的治疗效果明显改观 ,长期无病生存率大为提高。但随着生存期的延长 ,髓外白血病的发生逐渐增多 ,如何有效防治髓外白血病 ,已成为小儿 ALL治疗中的一大难题。为此 ,我们对应用大剂量甲氨喋呤 (MTX)预防髓外白血 In recent years, due to the continuous improvement of chemotherapy regimens, the therapeutic effect of pediatric acute lymphoblastic leukemia (ALL) has obviously improved, and the long-term disease-free survival rate has been greatly improved. However, with the extension of survival, the incidence of extramedullary leukemia gradually increased, how to effectively prevent extramedullary leukemia, has become a major problem in pediatric ALL treatment. To this end, we use large doses of methotrexate (MTX) to prevent extramedullary white blood