BackgroundThis study aimed to assess the treatment outcomes, toxicity, and potential prognostic factors in patients with early stage extranodal natural killer/T-cell lymphoma treated with radiotherapy combined with chemotherapy. MethodsOne hundred and eighteen patients with Stage I/II extranodal natural killer/T-cell lymphoma who were treated with radiotherapy combined with chemotherapy were retrospectively analyzed between July 2003 and January 2019. The median dose was 50 Gy (range, 45–61.2 Gy). The Kaplan–Meier method was used to calculate progression-free survival and overall survival. The patients were scored according to their prognostic indices. ResultsThe overall and complete response rates were 93.2% and 82.2%, respectively. At a median follow-up of 43 months, the 5-year overall survival and progression-free survival rates were 73.9% and 68.4%, respectively. Adverse events of grade 3 or higher was observed in 20 patients (16.9%). Patients with primary disease in the Waldeyer's ring had poorer survival (P=0.015). Compared with anthracycline-based regimens, non-anthracycline-based regimens significantly improved the 5-year overall survival (76.6% vs. 54.8%, P=0.027) and progression-free survival (72.4% vs. 53.1%, P=0.013). After treatment, the 5-year overall survival rate was 78.6% in complete response patients versus 44.9% in non-complete response patients (P=0.003). For patients with low-and intermediate-low-risk according to the nomogram-revised risk index model, the complete response rate was 100%. When primary lesion data were added to the nomogram-revised risk index as the basis for another prognostic index (modified nomogram-revised risk index), the low-risk (zero to two risk factors) and high-risk (three or more risk factors) categories were noted (84.2% vs 62.2%, P=0.036). ConclusionPatients with early stage extranodal natural killer/T-cell lymphoma had high response rates and favorable survival rates with radiotherapy and non-anthracycline-based chemotherapy regimens. Patients who achieved complete response had better survival than those who did not. The extranodal natural killer/T-cell lymphoma-specific prognostic models may require further optimization.