Inclusion Criteria:  Biopsy proved extranodal NK/T cell lymphoma No previous anti-cancer treatment Measurable lesion on baseline PET/CT and MRI Stage I Normal serum LDH level Primary tumor invasion (PTI) absence ECOG PS 0-1 Sufficient organ functions  Exclusion Criteria:  Other mature T- or NK- lymphoma Hemophagocytic lymphohistiocytosis Primary CNS lymphoma or CNS-involved lymphoma History of malignancy except for cutaneous basal-/squamous- cell carcinoma or cervical carcinoma in situ 3 years prior to study treatment