Radiotherapy Combined With GDP With or Without Chidamide in Stage I/II Extranodal Nasal NK/T-cell Lymphoma

Inclusion Criteria: 1. Diagnosis of NKTCL with typical morphology and immunophenotype, according to the 2008 World Health Organization classification of lymphomas; 2. no prior radiotherapy or chemotherapy; 3. age ≥ 18 years; 4. ECOG performance status 0-2; 5. Ann Arbor stages I and II; 6. tumors primarily occurring in the upper aerodigestive tract; 7. at least one unfavorable prognostic factor (age \> 60 years, B symptoms, elevated LDH, ECOG score 2, regional node involvement, and PTI); 8. at least one measurable lesion; 9. adequate hematological, hepatic, and renal functions; e.g., absolute neutrophil count ≥ 1.5 × 109/L, platelet count ≥ 80 × 109/L, total bilirubin ≤ 1.5 × upper limit of normal, alanine transaminase and aspartate transaminase ≤ 2 × upper limit of normal, and creatinine ≤ 1.5 mg/dl; 10. life expectancy of more than 3 months. Exclusion Criteria: 1. Patients with advanced stage disease; 2. pregnancy or lactation; 3. any coexisting medical problems of sufficient severity to prevent full compliance with the study protocol.