Gastrointestinal T- and NK-cell lymphomas and indolent lymphoproliferative disorders.

Primary gastrointestinal (GI) T- and NK-cell lymphomas constitute a heterogeneous group of uncommon and aggressive neoplasms, which have unique clinical and pathologic features. The intestines are the most frequent sites of disease, but almost any GI organ may be involved. Enteropathy associated T-cell lymphoma (formerly EATL type 1) and monomorphic epitheliotropic intestinal T-cell lymphoma (formerly EATL type 2) represent the two most common entities. However, other types of peripheral T-cell lymphomas can also occur in the GI tract or involve it secondarily. Moreover, indolent T- and NK-cell lymphoproliferative disorders (LPDs) of the GI tract have also recently been recognized. In this review, we describe the salient clinical, histopathologic, immunophenotypic, and molecular characteristics of primary GI T/NK-cell lymphomas and indolent LPDs, which form the basis for classification of the different entities, and an algorithmic approach to the diagnosis of these rare diseases.