Gammadelta T-cell lymphomas.

T-cell lymphomas expressing the gammadelta T-cell receptor (TCR) are uncommon, although their frequency may be underestimated. They show a broad clinicopathological spectrum. Besides precursor T-cell lymphoblastic leukemia/lymphoma, various post-thymic gammadelta T-cell neoplasms have been recognized. Among these, hepatosplenic gammadelta T-cell lymphoma constitutes the prototype of T-cell lymphomas expressing the gammadelta TCR and was listed as a provisional entity in the Revised European-American Lymphoma (REAL) classification. The recognition of this lymphoma subtype was further supported by the demonstration that the neoplasm results from a proliferation of nonactivated cytotoxic T cells and is associated with a recurrent cytogenetic abnormality, the isochromosome 7q. More recently, a few cases of hepatosplenic T-cell lymphoma with similar clinicopathologic features and alphabeta phenotype have been described that are thought to belong to the same entity, and the term "hepatosplenic T-cell lymphoma" is preferred in the current World Health Organization (WHO) classification. Most nonhepatosplenic gammadelta T-cell lymphomas occur in skin or in mucosal sites, a location that parallels that of normal gammadelta T cells. In contrast to hepatosplenic gammadelta T-cell lymphomas, they show an important clinical and morphological heterogeneity, have an activated cytotoxic phenotype, and are not believed to constitute a single disease entity.