KIT and mesenchymal cell neoplasm: GISTs are now defined as spindle cell, epithelioid, or occasionally, pleomorphic mesenchymal tumors of the gastrointestinal tract, which express the KIT protein (CD117) detected by immunohistochemistry and which lack smooth muscle or Schwann cells as seen in electron microscopy.[1] The term “GIST” is also limited to tumors originating from the pacemaker cells of Cajal located between myenteric plexus cells and smooth muscle cells of the GIT.