Biological and clinical review of stromal tumors in the gastrointestinal tract.

Submucosal tumors of the gastrointestinal tract (GI tract) mainly consist of gastrointestinal mesenchymal tumors (GIMTs) that are distributed in the GI tract from the esophagus through the rectum. GIMTs include myogenic tumors, neurogenic tumors and gastrointestinal stromal tumors (GISTs). The term "GIST" is now preferentially used for the tumors that express CD34 and KIT. GIMTs are composed of spindle or epithelioid cells, and 20% to 30% show malignant behavior, including peritoneal dissemination and hematogenous metastasis. KIT expression and mutations in the c-kit gene are found only in GISTs, but not in myogenic or neurogenic tumors. Mutation in the c-kit gene is associated with aggressive features and poor prognosis, and malignant GISTs frequently have mutations in the c-kit gene. The clinicopathological features of GISTs with or without c-kit mutations are markedly different. Therefore, GIMTs may be divided into four major categories based on histochemical and genetic data: myogenic tumors; neurogenic tumors; GISTs with c-kit mutation; and GISTs without c-kit mutation. The origin of GISTs is not fully understood. However, phenotypical resemblance to the interstitial cells of Cajal (ICCs) and gain-of-function mutations in the c-kit gene may suggest origin from ICCs and/or multipotential mesenchymal cells that differentiate into ICCs.