Gastrointestinal stromal tumor other diagnostic studies

Biopsy
A biopsy sample will be investigated under the microscope. The histopathologist identifies the characteristics of GISTs (spindle cells in 70-80%, epitheloid aspect in 20-30%). Smaller tumors can usually be found to the muscularis propria layer of the intestinal wall. Large ones grow, mainly outward, from the bowel wall until the point where they outstrip their blood supply and necrose (die) on the inside, forming a cavity that may eventually come to communicate with the bowel lumen.

When GIST is suspected&mdash;as opposed to other causes for similar tumors&mdash;the histopathologist can use immunohistochemistry (specific antibodies that stain the molecule CD117 (also known as c-kit) &mdash;see below). 95% of all GISTs are CD117-positive (other possible markers include CD34, desmin, vimentin and others). Other cells that show CD117 positivity are mast cells.

Some tumors of the stomach and small bowel referred to as leiomyosarcomas (malignant tumor of smooth muscle) would most likely be reclassified as GISTs today on the basis of immunohistochemical staining.