GISTs are the most common mesenchimal neoplasms of the gastrointestinal (GI) tract but are nevertheless rare tumors,
accounting for around 1% of all GI neoplasms.
Previously classified as GI leiomyomas and leiomyosarcomas,
because of the apparent origin from the muscularis propria layer of the intestinal wall,
GISTs are now known to be derived from interstitial cells of Cajal,
the pacemaker cells of the GI tract.
The pathogenesis is the result of activating mutations of the genes encoding promoting tumor survival and growth,
such as the receptor protein tyrosine kinase KIT (CD117 – expressed in 80-85%) or the platelet-derived growth factor receptor alpha (PDGFRA – expressed in 5-10%).
Moreover,
most GISTs express the CD34 antigen (70-80%) a hematopoietic progenitor cell antigen that occurs in a variety of mesenchymal tumors,
whereas smooth muscle actin (SMA) is positive in 20-40% of GISTs.
However,
independent of location,
the type of mutation has important therapeutic implications and can confirm the diagnosis even in doubtful cases,
therefore the mutational analysis should always be performed.
The median age is around 55–65 years,
equal in both male and female.
GISTs can occur anywhere along the GI tract,
including mesentery,
omentum,
and retroperitoneum,
even if rare.
The most common site of GISTs is the stomach (50-70%),
followed by the small bowel (30%),
and recto-colon (5-15%).
Less often,
GISTs are seen in the colon and oesophagus (1-5%).
Clinical presentation may vary depending on the size and anatomic location of the tumor: most GISTs show an indolent behavior,
often asymptomatic or incidentally detected.
Common presenting signs and symptoms are related to mass effect,
as abdominal pain,
palpable mass,
anorexia and dysphagia,
or related to tumor ulceration resulting in chronic or acute bleeding,
determining respectively anemia and faecal occult blood or melaena,
haematemesis or haematochezia,
depending on the amount of bleeding and tumor location in the GI tract.
In 10-30% of cases GISTs show malignant behavior manifesting both with local invasion and distant metastases,
most commonly spread to the liver,
from haematogenous seeding,
and throughout the peritoneal cavity,
from peritoneal seeding.
Metastases to lung,
bone,
lymph node and brain are uncommon.
The most frequent complications due to GISTs include: gastrointestinal bleeding,
intestinal obstruction,
and tumor perforation until massive rupture with haemoperitoneum or peritonitis; these conditions often determine an emergency status that requires an accurate preoperative diagnosis and urgent surgery.