<unk>  <unk> , previously termed<unk> , type I and at one time termed<unk> -type T-cell lymphoma (ETTL), is a complication of coeliac disease in which a malignant T-cell lymphoma develops in areas of the small intestine afflicted by the disease's intense inflammation. While a relatively rare disease, it is the most common type of primary gastrointestinal T-cell lymphoma.<unk>  had been defined as a single type of small intestine lymphoma, but in 2008, the World Health Organization (WHO) divided the disease into two subtypes: 1)<unk>  type I, which occurs in individuals with coeliac disease, a chronic immune disorder causing inflammatory responses to dietary gluten primarily in the upper reaches (i.e. jejunum and duodenum) of the small intestine; and 2)<unk>  type II, a disorder similar to<unk>  type I that occurs without coeliac disease. While type I and II<unk>  share many similar features, post-2008 studies found some significant differences between the two types. In 2016, the WHO redefined the two diseases as separate entities, keeping the term<unk>  for the coeliac disease-associated lymphoma and terming type 2 disease as monomorphic epitheliotropic intestinal T cell lymphoma (MEITL).<unk>  is five to ten times more common than is MEITL. The WHO also defined a third type of intestinal T-cell lymphoma that cannot not be classified as<unk>  or MEITL as peripheral T-cell lymphoma not otherwise specified (ITCL-NOS).<unk>  arises from the malignant transformation of small-intestinal intraepithelial lymphocytes (IEL). IEL are a heterogeneous group of principally T-cell lymphocytes residing in epithelial tissues that interface the environment, such as the mucosa of the bronchi, reproductive tract and gastrointestinal tract. At these sites, IEL are exposed and regulate immune responses to non-dietary and dietary antigens, pathogenic and non-pathogenic organisms and injured self tissues. Gastrointestinal tract IEL appear in the epithelium of the small intestine, colon, stomach and esophagus, residing between the epithelial cells that line these organs' lumens. These IEL often exhibit natural killer and cytotoxic T-cell cell activation markers, contain various toxic agents (e.g. perforin, granzyme) and therefore are capable, if activated, of causing severe tissue injuries. With coeliac disease, the IEL react to the glutelins in dietary gluten by increasing their numbers, becoming pathologically active, producing chronic inflammation that injures intestinal cells, interfering with nutrient absorption and creating an environment conducive to their malignant transformation into<unk> . Optimal treatment of<unk>  has used regimens consisting of intensive chemotherapy, hematopoietic stem cell transplantation and, in cases with bulky, obstructive and/or perforated bowel disease, surgical intervention. The disease has a five-year overall survival rate of only ~20%. However, recent studies focusing on the malignant IEL in<unk>  have increased understanding of the disease and suggested newer chemotherapy-based strategies and novel molecular targets that might be attacked therapeutically to improve the disease's prognosis.
Enteropathy-associated T-cell lymphoma
Monomorphic epitheliotropic intestinal T cell lymphoma
Hereditary progressive mucinous histiocytosis
MALT lymphoma
Natural killer cell enteropathy
Duodenal-type follicular lymphoma
Gastric lymphoma
AIDS-related lymphoma