P-glycoprotein is a product of the multidrug resistance (MDR1) gene, which is a major cause of the refractoriness of malignant lymphomas to conventional chemotherapeutic regimens containing anthracycline. l-asparaginase-containing regimens such as SMILE (steroid, methotrexate, ifosfamide, l-asparaginase, and etoposide) are effective for ENKL.