Two main types of intestinal T cell have been characterized.59 Type a mucosal T cells are mainly found in the ARN 077 lamina propria, and are mainly CD8-positive T cells, similar to those seen in the indolent T-cell LPDs. (iii) extranodal T-cell and NK-cell neoplasms; (iv) EBV-associated T-cell/NK- cell lymphomas/lymphoproliferative diseases; and (v) peripheral T-cell lymphoma, not otherwise specified, post-transplant lymphoproliferative disorders, and mimics. This report summarizes the discussions and conclusions of the workshop, which question current diagnostic criteria and provide recommendations for refining existing classifications. gene.2 However, in the absence of a specific genetic marker, the demarcation between ALK-negative ALCL and CD30-positive peripheral T-cell lymphoma, not otherwise specified (PTCL NOS), is less clear. Although the recent demonstration of distinct cytogenetic abnormalities in a proportion of the former validates classifying it as a distinct entity separate from PTCL NOS, these abnormalities are not universal.6 Another area of controversy in recent years has been the relevance of an versus a phenotype in defining T-cell ARN 077 lymphomas in a variety of sites.8 Other areas of uncertainty include the spectrum of Epstein-Barr virus (EBV)-positive T-cell and NK-cell lymphomas, for which diseases EBV expression is a defining feature, and how many categories should be recognized. Finally, it has become apparent that not all T-cell and NK-cell lymphomas are clinically aggressive, but the criteria for recognizing such cases are not yet fully established.9 The European Association of Haematopathology (EAHP) recognized the challenges and the recent phenotypic and genetic advances in the field of T-cell lymphoma diagnosis and research, and felt that there was a need to refine diagnostic criteria Rabbit polyclonal to HHIPL2 and clarify the borders between overlapping entities, and also to recognize potentially ARN 077 new entities. Therefore, a call was made for submission of cases for the lymphoma workshop of the XVIth meeting of the EAHP in association with the Society for Hematopathology (SH), Lisbon, 18C25 October 2012, under the title Peripheral T- and ARN 077 NK-cell lymphomas and their mimics; taking a step forward. Over 200 cases were submitted by participants worldwide, including a wide range of mature T-cell and T/NK-cell neoplasms/lymphoproliferations and their mimics. The cases were reviewed prior to the meeting by a panel of haematopathologists, using the submitted clinical and genetic information and available biopsy material. On the basis of this review, all submitted lymphoproliferations were grouped into five categories and presented in corresponding sessions at the meeting: AITL and T-follicular-helper-cell-associated lymphomas. CD30-positive T-cell lymphomas/lymphoproliferative diseases. Extranodal T-cell and NK-cell neoplasms. EBV-associated T-cell/NK-cell lymphomas/lympho- proliferative diseases. PTCL NOS, post-transplant lymphoproliferative disorders, and mimics. On the basis of the reviewed cases and the discussions at the EAHP/SH meeting, this article describes the diagnostic challenges, general conclusions and open issues in the field of peripheral T-cell and NK-cell lymphomas. Session 1: Angioimmunoblastic T-cell lymphoma and T-follicular-helper-cell- associated lymphomas AITL is an aggressive nodal peripheral T-cell lymphoma that usually presents with systemic symptoms, advanced-stage ARN 077 disease with generalized lymphadenopathy, frequent hepatosplenomegaly, and a pruritic skin rash, and is characteristically associated with immune dysregulation.2,10 Histologically, AITL shows effacement of nodal architecture by a polymorphous infiltrate, together with proliferation of high endothelial venules (HEVs) and follicular dendritic cell (FDC) meshworks, and frequent expansion of EBV-infected B-blasts.2 AITL may show three overlapping histological patterns (I, II, and III), with hyperplastic follicles, regressed follicles, and no identifiable follicles, respectively.11 Pattern I represents a perifollicular pattern of involvement, whereas patterns II and III are considered to betypical histology for AITL. For many years, the characteristic expansion of FDCs emphasized the importance of the follicular microenvironment in AITL. However, it is only in the last decade that gene expression profiling and phenotypic studies have shown that the neoplastic T cells of AITL are derived from TFH cells, a recently described distinct functional subset of mature T cells.3 The markers that are characteristic, but not always specific, for the TFH phenotype include PD1, ICOS, CXCL13, CXCR5, CD200,.