Differences in response to imatinib between gastrointestinal stromal tumours involving the liver and tumours that do not: experience from Nairobi Différences observées au niveau de la réponse au traitement par l'imatinib de tumeurs stromales digestives selon que lesdites tumeurs affectent ou non le foie : expérience conduite à Nairobi

Introduction: More than 60% of gastrointestinal stromal tumours (GISTs) arise from the stomach and about 20% from the small intestine. About 95% of GISTs express kit receptor tyrosine kinase (CD117), which is used for pur- poses of diagnosis and targeted treatment. However, kit expression alone is not specific for GIST, nor does it neces- sarily imply that signalling through the kit kinase is the driv- ing oncogenic event. Poor prognostic features of GIST include involvement of the liver and other bulky sites of disease. Patients and methods: We carried out a retrospective analy- sis of patients with CD117-positive leiomyosarcomas arising in the abdomen and treated through the Glivec International Patient Assistance Program (GIPAP) Clinic at the Nairobi Hospital between 7th November 2005 and 22nd November 2011. Results: In total 54 patients were included. Males were 36 (66.7%) and females 18 (33.3%). The age range was 25-86 years and the median age 50 years. The stomach was involved primarily in 22 of 47 cases evaluable (46.8%). The liver was primarily involved in 3 (6.4%) and liver metastases in 7 (14.9%) cases. None of 8 patients (0%) with evaluable liver involvement regressed or stabilized on treatment for at least 6 months compared with 10 of 14 (71.4%) from the stomach, 7 of 7 (100%) from the small bowel, and 7 of 13 (53.8%) with mesenteric/omental involvement. These differences were statistically significant (P<0.001). Conclusion: Apparent lack of response by tumours involv- ing the liver could suggest that the kit, or by extrapolation PDGFR-alpha overexpression, may not be the factors acti- vating kit or PDGFR-alpha targets in this subset of patients, or they could be of exon 9 mutation predominantly. Muta- tional analysis studies may shed more light in this issue.