Further characterization of c-KIT mutations and aberrant KIT localization in canine cutaneous mast cell tumors
Authors: Joshua Webster, Matti Kiupel, John Kaneene, Roseann Miller, James Resau, Vilma Yuzbasiyan-Gurkan
Journal: Cancer Research (2005)

1111  The c-KIT proto-oncogene encodes the receptor tyrosine kinase KIT, which has been implicated in the pathogenesis of multiple neoplastic diseases in people including gastrointestinal stromal tumors, small cell lung cancer, and germ cell tumors, and in the pathogenesis of cutaneous mast cell tumors (MCTs) in dogs. In contrast to human mast cell diseases, which are rare and frequently offer a good prognosis, canine cutaneous MCTs are one of the most common neoplasms in dogs and have an extremely variable biologic behavior ranging from a benign lesion to malignant metastatic disease. Due to the high frequency of canine MCTs and the known involvement of the c-KIT proto-oncogene in their pathogenesis, canine MCTs provide an excellent system to study the role of c-KIT in the development and progression of neoplastic diseases. Internal tandem duplication mutations (ITD) have been previously identified in the juxtamembrane domain of c-KIT in canine MCTs by our group as well as others. These mutations are predicted to result in a constitutively activated KIT protein. In order to study the role of c-KIT in canine MCTs, we have undertaken several studies to determine the associations between ITD mutations, cellular KIT protein levels, cytoplasmic KIT distribution, and patient survival. Here we report our studies on 60 cases of canine MCT with complete follow-up data. Laser capture microdissected samples of each tumor were analyzed using established PCR primers targeting the ITD region and aberrant products were sequenced. On each tumor KIT protein localization was assessed using immunohistochemistry. Representative samples of 42 MCTs were incorporated into a tissue array and the quantification of KIT protein was performed by measuring mean immunofluorescence of each tumor. 17.6% of the MCTs included in this study had ITD mutations and the KIT protein was aberrantly localized in 58% of the MCTs evaluated. The presence of ITD mutations was significantly associated with a decreased survival duration and disease free interval. There was a significant correlation between the presence of ITD mutations and aberrant localization of KIT protein in canine MCTs. The amount of KIT protein was not significantly correlated with the presence of mutations, or the cellular localization of KIT. The results of this study provide further support to the importance of activating mutations in c-KIT in tumorigenesis of MCTs and further suggest that ITD mutations may be responsible for a change in the cellular localization of KIT in canine MCTs. However, ITD mutations do not appear to be the sole candidate to be responsible for the aberrant localization of KIT in neoplastic cells. Understanding of the mechanisms that modulate cytoplasmic localization of c-KIT and the changes in cell signaling that may be occurring concomitantly or secondarily to this event will allow for a better understanding of the role of KIT in neoplastic processes.