Gastrointestinal Stromal Tumors (GIST)
2

GIST may show wide range of morphology

epithelioid cells (rounded cells)

mixture

Spindle stretched

Smooth muscle differentiation can be seen in these
tumors

very important because we need to
differentiate between GIST and the tumors that are
originally derived from smooth muscle which are
leiomyoma

95% of GISTs are positive for CD117 (c-KIT)
immunostain

to detect the gene

color the antibody with a brown color, this is why the
cells, which express this antigen, will be colored with
brown color, so the cells in brown color have the
CD117 (c-KIT) mutation

The Hematoxylin stain works in an opposite way, it colors the negative cells
(cells which lack the antigen)

Clinical picture:

the mass of tumor may affect the region where it
exists

depends on the size of the tumo

Asymptomatic

might affect the mucosa and lead to mucosal ulceration

Prognosis:

divided into risk categories (low – high) depending on

Tumor size.

Mitotic count per 50 HPF (high power field)

Location (gastric, esophageal or intestinal)

Metastases can appear after 20 years of removal of the original tumor, mainly
to liver.

Treatment:

Surgery

Targeted therapy like imatinib mesylate which is only targeted against
tyrosine kinase. That means they target only the cells that exhibit the mutation