Mutational Analysis of Gastrointestinal Stromal Tumors (GISTs): Procedural Approach for Diagnostic Purposes

Background: Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors in the digestive tract characterized, in the majority of cases, by activating mutations in the KIT (v-kit Hardy-Zuckerman 4 feline sarcoma viral oncogene homolog) or PDGFRA (platelet-derived growth factor receptor, alpha polypeptide) genes. Mutations affecting these tyrosine kinase receptors are also responsible for the mechanisms of primary and secondary drug resistance during the treatment with tyrosine kinase inhibitors. We performed mutational analysis to evaluate the pharmacotherapy susceptibility of GISTs, adopting a comprehensive procedural approach, in order to optimize the identification of mutations that may result in cellular resistance to conventional therapy. Materials and Methods: DNA from paraffin-embedded tumor sections from 40 GISTs were analyzed using microdissection, direct sequencing analysis and allelic separation by cloning. Results: KIT mutations were found in 55.0% of the tumor samples. PDGFRA mutations were present in 5.0% of cases. Allelic cloning assay allowed for better definition of the extent of the mutations and clarification of the exact nucleotidic position of complex mutations. Conclusion: Our experience suggests that sequential microdissection, direct sequencing and allelic separation by PCR cloning of large variants may improve the approach to mutational analysis and interpretation of sequence data of KIT and PDGFRA in patients with GIST.