Mutational Analysis of c-KIT and PDGFRA in Canine Gastrointestinal Stromal Tumors (GISTs)

SIMPLE SUMMARY: Gastrointestinal stromal tumors represent the most common mesenchymal tumor of the canine gastrointestinal tract. Activating mutations in c-KIT and PDGFRA genes are considered the key molecular drivers of human gastrointestinal stromal tumors pathogenesis and are used to predict the response to Receptor tyrosine kinase inhibitors. However, in veterinary medicine, the significance of these mutations in canine gastrointestinal stromal tumors has not been sufficiently explored yet. The aim of this study is to investigate the mutational status of c-KIT and PDGFRA, by PCR and sequencing, in 17 canine gastrointestinal stromal tumors. Mutations of c-KIT were detected in 47% of cases; in one case, PDGFRA mutation was also identified. Although follow-up data were not available for all specimens, based on the information collected, we observed at the time of diagnosis the presence of metastases in cases with c-KIT mutation. In conclusion, this study provides evidence for the presence of c-KIT and PDGFRA mutations in canine gastrointestinal stromal tumors and suggests a potential association of c-KIT mutation with the more aggressive biological behavior of the tumor. ABSTRACT: Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the canine gastrointestinal tract and are diagnosed by the immunohistochemical expression of the receptor tyrosine kinase (RTK) KIT. Activating mutations of the proto-oncogenes c-KIT and PDGFRA drive GIST oncogenesis and are used to predict the response to RTK-inhibitors in human oncology. Currently, the frequency and significance of these mutations in canine GIST have not been adequately explored. Therefore, we investigated the mutational status of c-KIT (exons 9, 11 and 13) and PDGFRA (exons 12 and 18) genes by PCR followed by fragment analysis for c-KIT deletions and PCR followed by screening with DHPLC and direct sequencing confirmation for single nucleotide variations in 17 formalin-fixed paraffin-embedded canine GISTs confirmed by KIT immunopositivity. c-KIT mutations were detected in 47% of cases, with a mutation detection rate significantly higher (p = 0.0004, Fisher’s exact test) and always involving exon 11. A PDGFRA gene mutation (exon 18) was identified in one case. Even if follow-up data were not available for all cases, four cases with documented abdominal metastases displayed c-KIT mutations. These data confirm that c-KIT exon 11 mutations occur frequently in canine GISTs, and identify the presence of a PDGFRA mutation similar to human GISTs. This study also suggests a potential association of c-KIT mutation with more aggressive biological behavior.