MKI67 and non-Hodgkin lymphoma: According to National Comprehensive Cancer Network (NCCN) guidelines for Non-Hodgkin's lymphoma version 2.2015, the risk factors for ENKTL include age>60 years, ECOG PS score≥2, B symptoms, increased LDH, regional lymphadenopathies, local tumor invasion, histological expression of Ki-67, Epstein-Barr virus (EBV) DNA > 6.1E+7/ml, and IPI score >2.