GIST is a rare form of sarcoma arising either from the interstitial cells of cajal (ICCs) or from less differentiated stem cells. The ICCs are located in the muscle layer of the gastrointestinal tract. GIST can occur anywhere but mainly affects the stomach (60%), jejunum and ileum (30%), duodenum (4–5%), rectum (4%), colon and appendix (1–2%) and oesophagus (<1%) . Rarely extra-gastrointestinal GIST occurs in the vicinity of the stomach or intestines . The overall incidence has been estimated at 10–20 per million.
There has been extensive study of GIST to determine whether tumour size, mitotic activity and genetic characteristics predict disease progression. GISTs more than 5 cm in size, independent of mitotic rate, have a moderate risk for metastases, and all tumours with less than 5 mitoses per 50 HPFs have a high risk for metastases. Miettinen and Lasota reasoned that when data are analysed by regression models tumour size may appear to show greater predictive value because mitotic count reaches a 'saturation point' when counts exceed 10 per 50 HPFs .
Bearzi et al  reviewed 158 cases of GIST. Only 12% of patients with a mitotic count over 10 per 50 HPFs remained disease-free after surgery, and all patients with a mitotic count over 20 per 50 HPFs experienced recurrence. They argued that if the combination of size and mitotic count place a tumour in the high-risk category, then the mitotic count might be the more indicative variable.
Recent papers suggest a mutation found in a GIST may predict its likelihood of recurrence. Emile et al  and Martin et al  identified specific mutations within c-KIT exon 11 which were associated with metastasis and poor prognosis. Several papers have found that patients with deletions in exon-11 rather than substitutions or duplications have a greater probability of recurrence or metastasis than other GIST patients [7, 8].
If these results are confirmed and expanded they could provide a rationale for identifying patients who need closer monitoring or perhaps adjuvant chemotherapy post-surgery to prevent recurrence rather than after the appearance of metastasis in line with guidance by the UK National Institute of Clinical Excellence (NICE; see Additional file 2).
Cell proliferation in a GIST is a result of the activation of growth factor receptors. KIT and platelet derived growth factor receptor alpha (PDGFRA) tyrosine kinases  are normally present on the ICCs. When the genes of these receptor cells are mutated activation take place without stimulation by the respective ligands (constitutive activation). This causes tumour growth.
Imatinib Mesylate (Glivec) is the first effective treatment for GIST. Imatinib binds to the intracellular activation pockets of the KIT and PDGFRA receptors in their inactive position, blocking their binding to ATP and preventing growth signals being sent, which stops disease progression. Drug response is related to the type of mutation of the c-KIT exon. Patients with the more common exon-11 mutation are most sensitive to imatinib  whereas patients with the exon-9-mutation, mostly found in those with small intestinal GIST, are the least sensitive .
The most commonly reported side effects of imatinib are nausea, diarrhoea, periorbital oedema, muscle cramps, fatigue, rash and headache. The most common serious adverse events are unspecified haemorrhage and neutropenia, each occurring in approximately 5% of patients (see Section 4.1.9 in ).
In our patient, imatinib was extremely effective in controlling the disease process. This was most likely a result of the type of mutation (exon-11) that was present in this tumour. The WHO performance status at diagnosis was three. Since September 2002, her WHO performance status has remained at zero. She had suffered from minor side effects of the drug like diarrhoea and watery painful eyes. She was reviewed in the oncology clinic and the change of regime to four weeks on and two weeks off the drug relieved these side effects.