Abstract

The cytogenic origin of canine transmissible venereal tumor (CTVT) still remains unknown.  Resulting from paucity of information on the histiocytic phenotypic features and behaviours of CTVT, this study was undertaken to show some uncommon cytomorphological features of CTVT and its immunoreactivity with S-100 protein. Nine cases of CTVT were investigated (6 females and 3 males) using nine fine needle aspirates for cytology and four biopsy samples for histopathology and immunohistochemistry. Cytology revealed CTVT cells with pale basophilic, fine granular cytoplasm and distinct intra-nuclear (3/9) and intra-cytoplasmic (9/9) vacuolations. Erythrophagocytosis by a giant binucleated CTVT cell in one dog and nuclear budding in 2 dogs were observed. Histopathology showed loose sheets and cords of uniformly round to ovoid cells with slight indistinct eosinophilic cytoplasm and a tendency towards glandular as well as syncytial formation. Nuclei were large and round with a single centrally placed nucleolus. The mitotic index was high. Immunohistochemistry of the four biopsy samples revealed negative immunoreactivity to pan-cytokeratin, actin and desmin but positive immunoreactivity with vimetin and S-100 proteins.  This is the first report in which CTVT showed erythrophagocytosis, nuclear budding and positive immunoreactivity to S-100 protein. Based on these cytomorphological and immunohistochemical features, we conclude that CTVT is of histiocytic/dendritic origin.

Keywords: Cytology, histopathology, Histiocytic origin, immunohistochemistry, Transmissible Venereal Tumour