Mature T-cell and NK-cell lymphomas in the pediatric age group.

Despite the overall rarity of T-cell and natural killer (NK)-cell neoplasms, these tumors are not uncommon in children. Anaplastic lymphoma kinase (ALK)+ anaplastic large cell lymphoma is the most common pediatric mature T-cell malignancy, usually having a good prognosis. Some cases with unusual clinical manifestations, such as a leukemic phase or central nervous system involvement, are more aggressive. ALK+ large B-cell lymphomas are rare in children and most commonly exhibit translocations involving ALK and clathrin. Notably, other malignant neoplasms encountered in the pediatric age group usually are derived from cytotoxic T cells or NK cells. These tumors are derived from cells of the innate immune system, comprising a more primitive type of immune response. Cases presented at the Society for Hematopathology and the European Association for Haematopathology workshop included examples of hepatosplenic gammadelta T-cell lymphoma, aggressive NK-cell leukemia, and fulminant Epstein-Barr virus-positive T-cell lymphoproliferative disease. This early component of the immune system might be targeted more often in pediatric hematologic malignant neoplasms, whereas tumors of the more mature adaptive immune system are more rare in children.