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The revised 2016 WHO classification considers several infrequent T-cell derived lymphoid entities and a heterogeneous group of lymphomas that cannot be categorized as any of the specific entities and for this reason are designated peripheral T-cell lymphomas not otherwise specified (PTCL, NOS). Most of them had already been included in the 2008 edition but the revised version has incorporated new data related to gene deregulation that are crucial to lymphomagenesis.

In this chapter, we will briefly outline the disease features of three lymphoma entities and of PTCL, NOS

Intestinal T-cell lymphomas

Intestinal T-cell lymphomas include the two main types of intestinal T-cell lymphoma considered in the 2008 WHO classification and designated enteropathy-associated T-cell lymphoma (EATL) type I, which is linked to coeliac disease, and EATL type II, which is not associated with this enteropathy. They are respectively designated, in the updated WHO classification, EATL and monomorphic epitheliotropic intestinal T-cell lymphoma (MEITL). A third type of intestinal T-cell lymphoma not otherwise specified (NOS) that cannot be classified as one of these two distinct subtypes and a new provisional entity designated indolent T-cell lymphoproliferative disorder (LPD) of the GI (gastrointestinal) tract have also been included in the 2016 revision [1].

EATL and MEITL have distinct epidemiology and genetic susceptibility and also differ in their immunophenotype and molecular genetics.

EATL is seen in individuals with coeliac disease and is strongly associated with certain HLA genotypes whilst MEITL is not. The former is seen in individuals from Western countries whilst MEITL is predominantly seen in Asian and Hispanic individuals. The main manifestations of EATL and MEITL are gastrointestinal such as nausea, vomiting, diarrhoea, bowel obstruction, weight loss and, rarely, perforation. About a third of patients have B symptoms. A haemophagocytic syndrome can be seen in EATL. Dissemination may occur to lymph nodes and rarely to lung, bone marrow and skin. In contrast to EATL and MEITL, which have an aggressive clinical course, patients with indolent T-cell LPD of the GI tract have an indolent clinical course; the lesions can involve the small intestine, oral cavity, stomach, colon or multiple sites [2].

EATL is characterized by intraepithelial involvement by pleomorphic medium-sized to large or anaplastic cells with prominent nucleoli admixed with histiocytes and eosinophils (Figures 24.1 and 24.2). Angioinvasion, angiocentricity and necrosis may be seen. The tumour spares the mucosa, which often shows villous atrophy. Precursor lesions are documented in patients with coeliac disease refractory to a gluten-free diet. These are subclassified as type 1 and type 2 refractory coeliac disease. In type 1, the intraepithelial lymphocytes have a normal CD3-positive, CD8-positive, T-cell receptor (TCR)-positive phenotype and the TR genes are polyclonal whilst in type 2 the lymphoid cells have an aberrant phenotype, have clonal TR genes and show the same chromosomal abnormalities that are seen in EATL. In MEITL, ...

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