Gastrointestinal stromal tumors (GISTs) are the most common (80%) mesenchymal neoplasms affecting the gastrointestinal tract (GI-tract) and represent about 5% of all sarcomas [1].
GISTs are usually solitary,
but may also be multiple in a small number of cases (Fig.1),
typically occuring in adults (median age of 55-60 years),
with an incidence rate of 10 to 20 new cases per million/year [2].
GISTs are defined as KIT-positive mesenchymal spindle-or-epithelioid-cells,
affecting the GI-tract,
omentum,
or mesentery.
It is now believed that GISTs are arisen from the interstitial cells of Cajal (ICC),
which are stem cells similar to pacemaker cells of the bowel wall.
They are characterized by expression of a tyrosine kinase growth factor receptor,
KIT (CD117) or mutations in the platelet-derived growth factor receptor α (PDGFRα) [3].
These immunohistochemical findings allow to obtain an accurate diagnosis and to distinguish these tumors from other mesenchymal tumors of GI-tract.
GISTs can arise anywhere in the GI-tract: 50-70% in the stomach (Fig.2-3),
25-30% in the small intestine (Fig.4-5),
5-10% in the colon-rectum (Fig.6),
< 5% in the esophagus (Fig.7).
The remaining may arise within the omentum or within the peritoneal layers (Extra-Gastro-intestinal Stromal Tumors,
EGISTs) (Fig.8-9) [4].
Malignancy in GISTs correlate with anatomical location,
size and it is significantly related to number of mitoses per high power field (HPF); nevertheless,
the tumor behavior is difficult do predict.
(Tab.1-2).
Benign GISTs are usually asymptomatic,
small in size,
characterized by a slow growing,
making difficult the detection of these tumors.
In this regard,
they are often incidentally detected during endoscopic or radiographic studies or during surgical procedures for other morbidities.
Usually,
benign GISTs appear as fixed and rounded masses of compact bundles of spindle cells,
arising from muscularis propria,
not covered by a true capsule.
Despite these characteristics,
they are easily detached from surrounding tissues.
Furthermore,
the detection of these tumors can be aided by deformation of the bowel wall.
Intussusception,
bleeding and ulcerations (typically single,
small and well-demarcated) are rather rare.
While,
malignant GISTs (greater than 10 cm in size and/or with mitotic counts greater than 5/50 HPF) are huge,
growing as large eccentric/extraluminal masses,
which may dislocate or deform adjacent structures.
Their progression is frequently degenerative,
characterized by necrosis,
calcification,
hemorrhage with acute hematemesis,
melaena or chronic anemia,
due to prominent arteries supplying the superficial layers.
Typical findings of malignancy include liver metastases and/or spreading to the entire abdominal cavity.
Lymph node involvement and lung or bone metastases are uncommon.