Further stratification of low-risk nasal NK/T-cell lymphoma by the presence of clinical or histologicrisk factors. Cases were stratified by one or more of the following clinical or histologic risk factors: hemoglobin < 11 g/dL, platelets < 150 × 10⁹/L, transformed cells > 40%, or Ki67 > 50%, after applying the (A) International Prognostic Index (IPI) or (B) Korean Prognostic Index (K-PI).