Recent Advances in the Diagnosis and Treatment of Natural Killer Cell Malignancies

SIMPLE SUMMARY: Natural killer (NK)/T-cell lymphomas are aggressive extranodal Epstein–Barr virus (EBV)-positive malignancies. They can be divided into three subtypes: nasal (involving the nose and upper aerodigestive tract), non-nasal (involving skin, gastrointestinal tract, testis and other organs) and disseminated (involving multiple organs). Lymphoma cells are positive for CD3ε, CD56, cytotoxic molecules and EBV-encoded small RNA. There is a predilection for Asian and Central/South American populations. Genome-wide association studies have identified lymphoma susceptibility loci in Asians. Positron emission tomography computed tomography and plasma EBV DNA quantification are crucial at diagnosis and follow-up. Stage I/II patients receive non-athracycline asparaginse-containing regimens, together with sequential/concurrent radiotherapy. Anthracycline-containing regimens are ineffective. Stage III/IV patients receive asparaginase-containing regimens, followed by allogeneic haematopoietic stem cell transplantation (HSCT). Autologous HSCT does not improve outcome. In relapsed/refractory patients, novel approaches include PD1/PD-L1 targeting, EBV-specific cytotoxic T-cells, and monoclonal antibodies. Small molecules including histone deacetylase inhibitors may be beneficial. ABSTRACT: Natural killer (NK)/T-cell lymphomas are aggressive malignancies. Epstein–Barr virus (EBV) infection in lymphoma cells is invariable. NK/T-cell lymphomas are divided into nasal, non-nasal, and disseminated subtypes. Nasal NK/T-cell lymphomas involve the nasal cavity and the upper aerodigestive tract. Non-nasal NK/T-cell lymphomas involve the skin, gastrointestinal tract, testis and other extranodal sites. Disseminated NK/T-cell lymphoma involves multiple organs, rarely presenting with a leukaemic phase. Lymphoma cells are positive for CD3ε (not surface CD3), CD56, cytotoxic molecules and EBV-encoded small RNA. There is a predilection for Asian and Central/South American populations. Genome-wide association studies have identified lymphoma susceptibility loci in Asian patients. Positron emission tomography computed tomography and plasma EBV DNA quantification are crucial evaluations at diagnosis and follow-up. Stage I/II patients typically receive non-athracycline regimens containing asparaginse, together with sequential/concurrent radiotherapy. Anthracycline-containing regimens are ineffective. Stage III/IV patients are treated with asparaginase-containing regimens, followed by allogeneic haematopoietic stem cell transplantation (HSCT) in suitable cases. Autologous HSCT does not improve outcome. In relapsed/refractory patients, novel approaches are needed, involving PD1/PD-L1 targeting, EBV-specific cytotoxic T-cells, and monoclonal antibodies. Small molecules including histone deacetylase inhibitors may be beneficial in selected patients. Future strategies may include targeting of signalling pathways and driver mutations.