<prompt> Answer this question truthfullyWhat is the staging of extranodal NK-T-cell lymphoma?  <response>: <reason> Extranodal NKT cell lymphoma survival rate is not well predicted by Ann Arbor staging system . A new system was introduced by a Korean study based on B symptoms, Ann Arbor system, LDH level, and regional lymphadenopathy combined.Four risk groups identified as below:Another parallel mechanism for extranodal NKT cell lymphoma is based on tumor biologic and micro-environmental factors. High Ki-67 nuclear antigen is a marker for actively proliferation tumor cell which could be a related factor with mass bulk. 