Adjuvant and Down-Staging Treatment with Imatinib in Gastrointestinal Stromal Tumours

Abstract: Background: GISTs are gastrointestinal mesenchymal tumours that express the type III receptor tyrosine kinase KIT. The KIT proto-oncogene encodes the receptor KIT. Most GISTs have gain-of-function mutations in the KIT or PDGFRA gene. The tyrosine kinase is therefore continuously activated leading to ligand-independent dimerization. Imatinib mesylate (Glivec®) is considered to be the first-line palliative treatment. The activated form of the KIT receptor tyrosine kinase is inhibited by imatinib. The aim of the study was to compare the survival of patients treated with either adjuvant or down-staging imatinib with historic controls treated with radical surgery (R0) only. Methods: A historic control group was chosen from a population-based series from western Sweden (population 1.6 million) that matched the adjuvant (n=23) and down-staging (n=7) groups respectively. Mutation analysis was performed in all cases with bidirectional direct sequencing. The recurrence-free survival was calculated. Results: There was only one recurrence (4 %) in the adjuvant group, and no recurrences in the down-staging study group, compared to 32/48 patients (67 %) in the control group. Tumour size decreased in diameter from 20 cm to 11 cm with down-staging treatment. Conclusion: Adjuvant imatinib improves recurrence-free survival in R0 resected patients. Down-staging treatment with imatinib is recommended for patients with large tumours or metastases. The importance of mutation analysis was established.