MEITL : Microscopic Features

The classification of intestinal T-cell lymphomas has been revised recently. The Enteropathy-associated T-cell lymphoma (EATL), type I is now simply called EATL. Type II EATL is now labeled Monomorphic Epitheliotropic Intestinal T-cell Lymphoma (MEITL). Both types are aggressive, seen mostly in adults, and are EBV-negative. The full spectrum of intestinal T-cell lymphomas includes: EATL: It is closely linked to celiac disease and is more common in individuals of Northern European descent. The cellular infiltrate is polymorphic. The neoplastic T-cells express alpha-beta T-cell receptor, but rare cases of gamma-delta do occur. MEITL: It is not associated with celiac disease and is more common in Asian and Hispanic populations. It is composed of CD8+, CD56+ monomorphic infiltrate. It expresses megakaryocyte-associated tyrosine kinase (MATK) and shows gains in 8q24 involving MYC. Most cases express gamma-delta T-cell receptor. Mutations in STAT5B and SETD2 are commonly seen. Intestinal T-cell Lymphoma, NOS: Includes cases that don't meet the criteria for either EATL or MEITL. Indolent T-cell Lymphoproliferative Disorder of the Gastrointestinal Tract: An indolent, low-grade tumor that presents as mucosal infiltration (usually small bowel) by small mature-appearing CD8+ lymphocytes. Reference: Revised 4th Edition of WHO Classification of Tumors of Hematopoietic & Lymphoid Tissues, 2017.