Ekspresija antigena ćelijske proliferacije na mastocitima i njihov značaj za gradaciju mastocitoma pasa / Expression of proliferating cell antigens on mast cells and their significance for mast cell tumor classification

Cutaneous mast cell tumours (MCTs) are one of the most common neoplasm in dogs. Originate from the bone marrow, from the mast cells line, but because of its location are being studied within skin tumors. MCTs show a highly variable biologic behavior and therefore several criteria have been proposed for their classification, including histological grading and cell proliferation markers. Cytoplasmic expression of CD117 or KIT protein (tyrosine kinasa receptor) has been found to correlate with higher histological grade and with a worsened prognosis. It has been revealed that there is a conection between the aberrant expression of CD117 and presence of c-kit mutations, although mutations were not present in all mast cell tumors with aberrant expression of KIT protein. Twenty four MCTs and 6 control specimens from 30 dogs of different age, breed and sex were included in this study. DNA isolated from the dog with mast cell tumor which had previously found to has specified mutation was used as a positive control for c-kit mutation. Formalin fixed and paraffin embedded tissue samples were stained with hematoxylin-eosin and toluidin blue and immunohistochemically tested for CD117, Ki-67, PCNA i CD45RA expression. DNA had been extracted from the same paraffin blocks and subsequent polymerase chain reaction amplification was performed using PE1 and PE2 primers. Fourteen of 24 MCTs were histologically high-grade, while ten were classified as a low-grade malignancy. Seven MCTs have more than six mitotic figures in 10 high-power fields. The presence of more than two multinucleated cells in 10 high-power fields was observed in 11 MCTs, while more than two cells with bizarre nuclei in 10 hpf were observed in 10 MCTs. Eight MCTs have more than 10% of neoplastic mast cells with nuclei about 8-10 microns in diameter. Of the total MCTs, 9 tumors are Ki-67 positive (7 mastocytomas of high and 2 mastocytomas of low-grade malignancy), while the expression of PCNA and CD45RA was observed in all 24 MCTs. Nine MCTs of high-grade malignancy showed aberrant cytoplasm labeling for CD117. Mutations of c-kit proto-oncogene were not detected in any of the tested MCTs. The presence of mitotic figures, multinucleated cells, bizarre nuclei and karyomegaly in 10 high-power fields, as well as the pattern of CD117 expression are prerequisite for the new classification and most important prognostic factor in dogs with mast cell tumor.