Biology and management of rare primary extranodal T-cell lymphomas.

Peripheral T-cell lymphomas (PTCLs) are uncommonly encountered malignancies in the United States, and hepatosplenic T-cell lymphoma (HSTCL), subcutaneous panniculitis-like T-cell lymphoma (SPTCL), and enteropathy-type T-cell lymphoma (ETTCL) are rare subtypes of PTCLs that often present with primarily extranodal disease. Despite the fact that these tumors have distinct clinical and pathologic features, they are often diagnosed after significant delay. The combination of delay in diagnosis with ineffective therapies has resulted in a poor prognosis in most cases. Techniques that identify T-cell receptor gene rearrangements and flow cytometry that can identify characteristic immunophenotypes have guided our understanding of the underlying cell of origin of these rare PTCLs. As knowledge regarding the biology of these lymphomas increases alongside the development of newer therapeutics with novel mechanisms, clinicians must accordingly improve their familiarity with the clinical settings in which these rare malignancies arise as well as the pathologic features that make them unique.