Background: Extranodal natural killer (NK) / T cell lymphoma is a subtype of non-Hodgkin’s lymphoma (NHL) that usually has an aggressive clinical course. It is the predominant trigger of lymphoma-associated hemophagocytic syndrome (LAHS), which is highly lethal and with extremely poor prognosis. This study is aiming to characterize the associated clinical features and prognostic factors of the disease. 
Patients and methods: Twenty-eight patients with extranodal NK/T cell lymphoma associated hemophagocytic lymphohistiocytosis (HLH) were retrospectively analyzed. The clinical records were collected, and the associations between clinical or laboratory parameters and overall survival (OS) were assessed. 
Results: The most frequently clinical characteristics were fever (96.4%), and splenomegaly (81.5%). Concerning the laboratory findings, the most common features were hyperferritinemia (91.7%), grade III/IV thrombocytopenia (64.3%), hypertriglyceridemia (48%), severe anemia (46.4%), hypofibrinogenemia (45%), and grade III/IV neutropenia (32.1%). The interval between the diagnosis of NK/T LAHS and death / last contact was between 4 to 701 days with the median interval of 15 days. We found that higher serum lactic dehydrogenase (LDH) at HLH, hypofibrinogenemia, and splenomegaly were significantly associated with worse survival (P =0.002, 0.003, 0.003). Furthermore, Eastern Cooperative Oncology Group (ECOG) score, extra-upper aerodigestive tract NK/T cell lymphoma (EUNKTL) and cutaneous involvement were risk factors of HLH. 
Conclusion: Our data indicated that levels of LDH, fibrinogen, and presence of splenomegaly were prognostic factors of the disease. Higher ECOG scores, EUNKTL and cutaneous involvement were risk factors of NK/T LAHS. Additional independent, prospective clinical trials will be needed to explore optimal treatment.
Keywords: NK/T-cell lymphoma, hemophagocytic lymphohistiocytosis, risk factor, prognosis