Gastrointestinal Stromal Tumour (GIST)

Question 1

Pathology

Answer 1

• arise from interstitial cells of Cajal (ICC), the pacemaker of GIT (autonomic nervous system)
• tumour has appearance of neural tissue
• appear as small tumour within muscular wall or large tumour growing out from bowel wall (outstrip blood supply and become partly cystic)

Question 2

Aetiology

Answer 2

• a/w type I neurofibromatosis
• spontaneous mutation in c-kit gene (code for transmembrane receptor for stem cell factor)
• c-kit mutation–> continuous signal for cell growth mediated via tyrosine kinase in intracellular domain of molecule
• arise from mutation in platelet-derived growth factor receptor alpha

Question 3

special investigation

Answer 3

• endoscopy: detect tumour which appear submucosal polyp and ulcerated surface
• CT: identify presence of tumour
• endoscopic ultrasound: confirm nature of polyp and demonstrate origin of polyp from muscular layer of stomach wall
• positron emission tomography (PET): detection and staging of tumour
• percutaneous biopsy: in presence of metastases, presence of c-kit protein (CD117) on cell surface

Question 4

treatment

Answer 4

• surgical: wide excision
• chemotherapy: imatinib mesilate (Glivec), prior to surgery, to shrink large tumour to make it operable or postoperatively to treat metastases or when complete resection was not possible