A RETROSPECTIVE STUDY OF CANINE SKIN ROUND CELL TUMOURS Radostin Simeonov Department of General and Clinical Pathology, Faculty of Veterinary Medicine, Trakia University, Stara Zagora, Bulgaria, e-mail: rsimeonov@uni-sz.bg ABSTRACT А pathohistological analysis of 430 specimens of canine skin tumours obtained in the period 2000-2010, was performed at the Department of General and Clinical Pathology, Faculty of Veterinary Medicine, Trakia University, Bulgaria. Among the total number of skin tumours, 35 types of cutaneous neoplasms were diagnosed. The most predominant tumours were the epithelial and melanocytic tumours (58.13 %), followed by round cell (23.72 %) and mesenchymal tumours skin and soft tissue tumours (18.4 %). The ratio of benign to malignant neoplasm was 48.14 to 51.86. The most frequently diagnosed skin round tumours were mastocytoma (10.35 %) and histiocytoma (8.19 %). Keywords: skin, round cell tumours, dogs, incidence INTRODUCTION Skin and subcutaneous tumours are the most frequent kinds of such a disease known to affect dogs, accounting for one third of all cases in this species (Brodey, 1970; Finnie & Bostock, 1979; Bostock, 1986; Rotthwell et al., 1987). The incidence of cutaneous tumours in dogs is estimated to be 450 cases every years per 100000 dogs (Bostock, 1986; Priester, 1979). The aetiology of canine skin and subcutaneous tumours is unknown. Most authors connected higher incidence rates with exposure of different unfavourable environmental factors (Bostock, 1986; Guzman et al., 2003; Meleo). The age of the dogs with diagnosed skin tumours is commonly reported to range widely between 4 months and 16 years, although the average age is approximately 9 years (Brodey, 1970; Finnie & Bostock, 1979). The main reason of this study was to determine prevalence and distribution of canine round cell tumours between 2000-2010 at the Department of Pathology, Faculty of Veterinary Medicine, Trakia University, Stara Zagora, Bulgaria. MATERIAL AND METHODS Animals and tumours The study was performed at the Department of Pathology, Faculty of Veterinary Medicine, Trakia University, Bulgaria. Four hundred and thirty samples of spontaneous skin tumour growths in dogs originating from various regions of the country, were studied (2000-2010). Among the biopsy specimens, 102 cases (24 %) were diagnosed as skin round cell tumours and were included in this study (Table. 1). The study included dogs of all breeds and both sexes (47 male dogs and 55 bithes), with their age ranging between 4 months and 12 years. Histopathologic examination For histopathologic examination, the tissues were fixed in 10 % phosphate-buffered neutral formalin, routinely processed, paraffin embedded, and stained with haematoxylin and eosin (H&E). Replicate sections of particular cases were also stained with special stains such Azan trichrome, Mallory trichrome, Methyl green pyronin, PAS, Tоluidine blue whenever they were needed to confirm the diagnosis. All tumour s diagnoses were histopathologically confirmed according to WHO International Histological Classification of Tumours of Domestic Animals (Goldschmidt et al., 1998). Immunohistochemical detection of cytokeratin, vimentin, desmin, E-cadherin, Tryptase and CD 117 was performed using a two step technique (streptavidin-biotin-lsab ± Dako) with DAB chromogen. Animal studies & Veterinary medicine 13
RESULTS Out of the total 430 skin tumours from dogs (2000-2010), canine skin round cell tumours were diagnosed in 102 cases, i.e. in 47 (46.08 %) male animals and 55 (53.92) bithes, age approximately 7.3 years (ranging from 4 months to 12 years). Based on the final diagnosis out of 430 cutaneous neoplasms 223 (51.86 %) were malignant, while 207 (48.14 %) were benign tumours. The most predominant neoplasms in the studied material were epithelial and melanocytic tumours (58.13 %), followed by round cell (23.73 %) and mesenchymal skin and soft tissue tumours (18.14 %). Canine mastocytomas represented 10.35 % of all neoplasms included in this study (Table 1). They had a highly variable gross appearance (Fig. 1). The average age of affected dogs was 7 years, varying from 4 to 12 years. The neoplasms were located on the head and neck (40.9 %), trunk (40.9 %) and extremities (18.18 %). Histologically the cells were round to polygonal with round central to slightly eccentric nuclei and moderate, pale pink cytoplasm containing granules (Fig. 2). Mastocytomas were classified as grades (I to III) on the basis of the histopathologic grading criteria of Patnaik et al. (9). Histiocytomas are benign tumours, extremely common and unique to dogs. The average age of affected animals was 5 years, varying from 4 months to 6 years. The tumours were located on the head and neck (82.85 %), trunk (14.28 %) and extremities (2.82 %). In macroscopic appearance tumours had button shape (Fig. 3). Histologically there was dermal infiltrates of packed, mildly pleomorphic, round cells. The neoplastic cells looked histiocytic (Fig. 4). Mitotic figures were numerous. Most of the lymphomas in our record were located on the trunk (54.55 %) and average age of affected animals was 10 (8-12) years (Fig. 5). Histologically there were two forms epitheliotropic and nonepitheliotropic (Fig. 6). The majority of cutaneous plasmacytomas in our study occurred in older dogs (7-12) years. Most tumours were single, small, slightly raised dermal nodules covered by alopecic, occasionally ulcerated skin. The pinnae and digit were preferentially affected (60 %). Histologically sheets of round cells with pleomorphic nuclei were seen in poorly defined cords and nests. These cells could be in different shape and at low magnification these served as a useful diagnostic marker for this neoplasm (Fig. 7). Most neoplasm cell did not have typical plasma cell clock face nuclear chromatin pattern. The mitotic index was low. In our record we had a case with cutaneous malignant histiocytosis. The patient was female Golden Retriver at the age of sixth. Skin lesions were multiple; the dog had metastases (observed ultrasonographically, and subsequently confirmed histologically) in internal organs. Histologically there were a multifocal to diffuse infiltrates of large round to polygonal cells with ovoid to reniform nuclei and abundant eosinophilic cytoplasm. The cells formed loose sheets with little or no stroma. Some cells resembled normal macrophages, but others showed marked variation in size and shape. Multinucleate forms were often present with marked nuclear atypia. In one case we observed transmissible venereal tumour in 8 year Boxer bitch. The tumour was located in the vulvar area. The surface was ulcerated. Histologically, the tumour was composed of rows and cords of comparatively uniform round to ovoid cells. Nuclei were large, round and cell margins were indistinct. The cytoplasm was of moderate amount, light pink to clear in appearance (Fig. 8). The cells had high mitotic index and different numbers of mononuclear cells infiltrated the tumour. DISCUSSION Out of the total number of tumours investigated for the period 2000-2010 at the Department of Pathology skin tumours are the second most frequent neoplasms with an incidence of 33 %, preceded minimally only by mammary gland tumours (35 %), which is consistent with the finding of others investigators (Finnie & Bostock, 1979; Benjamin et al., 1999; Moulton, 1990; Dinev, Animal studies & Veterinary medicine 14
2002; Kovacevic, 2005, Tzvetkov, 1998). However, according to the other authors these tumours are the most frequent with an incidence of 1.437 cases per 100000 dogs per year (Dobson et al., 2002). The most frequent neoplasms in our study were epithelial and the melanocytic skin tumours (58.13 %), followed by round cell (23.73 %) and mesenchymal skin and soft tissue tumours (18.14 %). These findings differ from the results reported by other authors (Chalita et al., 2001; Kaldrymidou et al., 2005). Out of the total of 430 canine cutaneous tumours 223 (51.86 %) were malignant, while 207 (48.14 %) were benign. This is in agreement with the finding of Kovacevic et al. (13). However, based on the findings reported by Kaldrymidou et al. (17) malignant cutaneous accounted for 46.6 %, while benign tumours accounted for 53.4 %. Bostock et al. (3) reported the total number of malignant cutaneous neoplasms to be approximately 40 %. The results from investigation of Pakhrin et al. (18) are similar. The sex predilection of investigated canine round tumours of skin and soft tissues was not significantly different (male 46.08 % versus female 53.92 %) in 102 total cases. By respect to age-related incidence, our data are very close to those of most researchers. The localization of tumour growth is also analogous to that, already reported (Patnaik et al., 1984; Dinev 2002; Kovacevic, 2005; Chalita et al., 2001; Pakhrin et al., 2007). It is very important for practising vets to provide additional information with submitted material for pathohistological investigation (Pakhrin et al., 2007; Vail & Withrow, 2001). The protocol should include history of disease and detail description of macroscopic finding (duration and neoplastic rate, change in consistence and colour, and presence or not of metastases). Table 1. Incidence of canine skin round cell tumours diagnosed at the Department of General and Clinical Pathology of Animals over the investigated period. Tumour diagnosis Number % out of all cutaneous tumours Cutaneous round cell tumours 102 23.72 % Mastocytoma 44 10.23 Histiocytoma 35 8.13 Lymphoma 11 2.55 Plasmacytoma 10 2.32 Malignant fibrous histiocytosis 1 0.23 Transmissible Venereal Tumour 1 0.23 Fig. 1. Macroscopic view of cutaneous mastocytoma. Animal studies & Veterinary medicine 15
Fig. 2. Microscopic view of canine mastocytoma. The neoplastic cells are CD 117 positive (arrows). Fig. 3. Macroscopic view of cutaneous histiocytoma after surgical removal. Animal studies & Veterinary medicine 16
Fig. 4. Cutaneous histiocytoma. H/E staining. Fig. 5. Cutaneous epitheliotropic lymphoma in a dog. Animal studies & Veterinary medicine 17
Fig. 6. Cutaneous epitheliotropic lymphoma. The neoplastic lymphocytes are strong CD 3 positive. Fig. 7. Cutaneous plasmacytoma. The cytoplasm of plasma cells are pink-red (arrows). Methyl green pyronin staining. Animal studies & Veterinary medicine 18
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