What Is Needed to Diagnose GIST? Usually gastrointestinal
stromal tumor (GIST) is diagnosed from the features of the cells
that comprise the tumor tissue with confirmation of the
expression of the protein KIT (also called CD117) in the tumor
cells, along with other proteins, by immunohistochemistry (a
special laboratory technique to detect proteins in cells). In
addition, certain proteins are very rarely expressed by GIST,
such as desmin, and the absence of these proteins can also be
useful diagnostically. Although a few other abdominal tumors can
rarely test positive for KIT, the pathologist can use the
results from a panel of tests to differentiate among the
possible diagnoses. Those few GISTs that are negative for KIT
can be identified by an expert pathologist using cell
characteristics and the pattern of results for the panel of
tests. Newer protein markers such as DOG1 (which stands for
discovered on GIST 1) can also be helpful for diagnosis. What is
KIT (CD117)? KIT protein (or CD117) is a cell-surface