TY - CHAP M1 - Book, Section TI - Gastrointestinal Mesenchymal Tumors A1 - Ursem, Carling A1 - McQuaid, Kenneth R. A2 - Papadakis, Maxine A. A2 - McPhee, Stephen J. A2 - Rabow, Michael W. A2 - McQuaid, Kenneth R. Y1 - 2022 N1 - T2 - Current Medical Diagnosis & Treatment 2022 AB - Gastrointestinal mesenchymal tumors (which include stromal tumors, leiomyomas, and schwannomas) derive from mesenchymal stem cells and have an epithelioid or spindle cell histologic pattern, resembling smooth muscle. The most common stromal tumors are gastrointestinal stromal tumors (“GISTs”), which originate from interstitial cells of Cajal. GISTs occur throughout the gastrointestinal tract, but most commonly in the stomach (60%) and small intestine (30%). Approximately 80% of GISTs have mutations in KIT, a receptor tyrosine kinase that binds stem cell factor, or a homologous tyrosine kinase, platelet-derived growth factor alpha that lead to constitutive kinase activation. Approximately 95% of stromal tumors stain positively for CD117 (part of the KIT protein). The presence of multifocal GISTs is associated with neurofibromatosis-1. Other mesenchymal tumors, such as leiomyomas, which derive from smooth muscle cells, generally stain negative for CD117. A percentage of the KIT wild type tumors have a mutation in PDGFRA, and only a minority of patients are wild type for both genes. Mesenchymal tumors may be discovered incidentally on imaging studies or endoscopy or may cause symptoms (most commonly bleeding, pain, or obstruction). At endoscopy, they appear as a submucosal mass that may have central umbilication or ulceration (eFigure 39–6). EUS with guided FNA biopsy is the optimal study for diagnosing gastric mesenchymal tumors and distinguishing them from other submucosal lesions. Percutaneous biopsy may confer risk of bleeding or intra-abdominal seeding. CT of the abdomen and pelvis with contrast, MRI, and PET imaging are useful in the diagnosis and staging. PET imaging also may be useful to monitor response to treatment. SN - PB - McGraw-Hill Education CY - New York, NY Y2 - 2024/03/29 UR - accessmedicine.mhmedical.com/content.aspx?aid=1184389736 ER -