Currently, combined chemotherapy (CT) and radiation (RT) is recognized as the standard treatment for high-risk early-stage NKTCL. However, treatment failure occured in nearly 30% of patients receiving CRT and systemic failure are the most common failure form. Chidamide is a HADC inhibitor, which presents satisfactory efficacy in NKTCL especially in terms of improving durable remission time. In our previous study, IMRT followed by GDP was demonstrated effective in early-stage NKTCL. Therefore, we designed a prospective phase II clinical trial of IMRT followed by GDP with or without chidamide in patients with high-risk early-stage NKTCL.

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.