EBV-associated T and NK cell lymphoproliferative disorders: Consensus report of the 4th Asian Hematopathology Workshop

T and NK cell proliferative diseases associated with acute and chronic Epstein-Barr virus (EBV) infection are uncommon and raise several clinical issues regarding diagnostic criteria and terminology. This is a summary report of the consensus meeting held in the 4th Asian Hematopathology Workshop. The umbrella term "EBV-positive T/NK lymphoproliferative disease in childhood-type" covers the entire spectrum of EBV-associated lesions in childhood, ranging from reactive to neoplastic processes. Systemic T/NK cell lymphoproliferative disease (LPD) of childhood type is defined as a fulminant disease associated with the proliferation of polyclonal, oligoclonal, or monoclonal T or NK cells and includes aggressive NK cell-associated leukemia in children. Chronic active EBV disease-type T/NK cell LPD is divided into three groups-polymorphic/polyclonal, polymorphic/monoclonal, and monomorphic/monoclonal-based on the histology and clonality of T or NK cells. A monoclonal EBV-positive T/NK cell type of proliferation with the clinical features of chronic active EBV disease rather than the fulminant course of systemic EBV-positive T/NK cell LPD of childhood is considered "chronic active EBV disease-type T/NK cell LPD". Hydroa vacciniforme (HV)-like T cell LPD is defined as a spectrum of EBV-infected T cell proliferative diseases with homing to the skin and is further classified into a classic type, a severe type, and malignant lymphoma. Criteria to define each category of HV-like T cell LPD remain to be clarified.