IMPORTANT HISTOLOGICAL AND IMMUNOCHEMICAL PARAMETERS FOR CLASSIFICATION OF CANINE MAST CELL TUMORS

Mast cell tumors (MCTs) are one of the most common neoplasms indogs. They originate from the bone marrow. Several criteria have been proposedfor their classification, including histological grading and cell proliferation markers.The mitotic index, multiple nuclei, cells with bizarre nuclei and karyomegaly are themost important parameters for the classification of MCTs on high and low-grademalignancy. For the confirmation of MCT malignancy grade it is also important todetermine the expression of the transmembrane kinase (KIT) receptor that has asignificant role in the growth and differentiation of mast cell tumors. In high-grademalignancy MCTs in addition to membrane expression of the KIT receptor, aberrantcytoplasmic expression can be also observed. Fifty-two MCTs and 12 controlsamples of skin from dogs without MCTs were examined. Routinely processed tissuesamples were stained with hematoxylin-eosin. Expression of KIT receptor wastested immunohistochemically. The classification of MCTs on high and low-grademalignancy was performed according to the Kiupel’s 2-tier classification and theexpression of KIT receptors. Sixteen of 52 MCTs were of a low-grade malignancy,while thirty-six were classified as a high-grade malignancy of which 19 MCTsshowed aberrant cytoplasm labelling of KIT receptor. All 16 low-grade malignancyMCTs had only membrane expression of KIT receptor. Most high-grade malignancyMCTs showed cytoplasmic KIT expression indicating the link between aberrantKIT expression and increased cell proliferation. The presence of mitotic figures,multinucleated cells, bizarre nuclei and karyomegaly, as well as KIT receptorexpression pattern are the most important prognostic factors in dogs with mast celltumor