Carcinosarcoma. Masson's Trichrome stain. 

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... periodic acid-Schiff (PAS) and Masson's Trichrome whenever they were needed to confirm the diagnosis. All tumour's diagnoses were histopathologically confirmed according to WHO Histological Classification of Mammary Tumors of the Dog and Cat (Misdorp et al., 2001). Based on the final diagnosis out of 456 canine mammary gland neoplasms 256 (56 %) were malignant, while 200 (44 %) were benign tumours. Among the biopsy specimens, 30 (65.78 %) cases were diagnosed as epithelial tumours, 55 (12.06 %) were diagnosed as mesenchymal tumours and 101 (22.16 °/о) cases were diagnosed as mixed tumours (Tabl. 1). The most frequently diagnosed benign epithelial tumours were cystadenomas (13.15 %) and fibroadenomas (6.14 %) The most frequently diagnosed malignant epithelial tumours were tubulopapillary carcinomas (26.31 %) and solid carcinomas (6.79 %) followed by anaplastic carcinomas (2.63 %) and squamous cell carcinomas (2.41 %). Pathoh istologically, benign mammary tumours were always surrounded by thin fibrous capsule and with parenchyma consisting from both epithelial and mesenchymal cell components. Simple adenomas may be of tubular type, consisting of well-differentiated luminal epithelial cells. Some of the tumours had a secretory products. Complex adenomas were composed of luminal epithelial cells together with spindle shaped or stellate cells resembling myoepithelial cells. Fibroadenomas consisted of a mixture of luminal and fibroblast stromal cells, sometimes admixed with myoepithelial cells (Fig. 1). Benign mixed tumours were composed of benign cells resembling epithelium and myoepithelium mixed with mesenchymal cells that have produced fibrous tissue in combination with cartilage, bone and/or fat (Fig. 2). Tubulopapillary carcinomas were characterized by the formation of tubules with or without papillary projections (Fig. 3). The stroma l component was usually scanty. Neoplastic cells in solid carcinomas were arranged in solid sheets, cords, or nest (Fig. 4). The amount of stroma ranged from small to moderate. Anaplastic carcinomas were composed of large pleomorphic cells, often with bizarre nuclei that are rich in chromatin. Some cells were multinucleated. The most frequently diagnosed canine mammary gland mesenchymal tumours were fibromyxomas (2.85 %), fibrosarcomas (2.61 %) and osteochondromas (2.41 %). The other neoplastic types varied between 0.75 % and 1.31 %. Fibromyxomas had both fibrous and myxomatous elements. Fibrosarcomas were composed of neoplastic spindle cells that have formed reticulin and colagenous fibers (Fig. 5). Osteosarcomas were characterized by osteoid production by neoplastic cells. Pleomorphism and mitotic activity were usually prominent. Carcinosarcomas were composed of cells morphologically resembling malignant epithelial cells (luminal epithelial and/or myoepithelial) and cells resembling malignant connective tissue (Fig. 6). Out of the total number of tumours examinated for the period 2000-2010 at the Department of Pathology mammary gland tumours are found to be the most frequent neoplasms with an incidence of 35 %, following by skin neoplasms (33 %), which is consistent with the finding of others authors (Finnie & Bostock, 1979; Benjamin et al., 1999; Moulton, 1990; Dinev et al , 2002; Kovacevic et al., 2005). Recently, a tendency toward progressive increase in malignant tumour incidence on the account of benign ones was noticed, as well as towards a relatively younger age of dogs affected by benign neoplasms (Perez Alenza et al., 1998; Perez Alenza et al., 2000; Gourley, 2000, Dinev et al., 2002). At 9 to 11 years of age, dogs have maximum risk of developing mammary tumours, although the risk rises at the age of 6 to 11 years (Schneider et a., 1969; Moulton, 1990). The results of investigation of Dinev et al., 2002 in Bulgaria showed a considerable increase in the number of mammary tumours since 1996 with peaks in 1998 and 1999. Those data are in accordance with the existing tendency towards progressive increase in this neoplastic kind in the bitch and the neoplastic incidence in general ( Zhelev et al., 1966; Tzvetkov, 1998; Perez Alenza et al., 2000; Restucci et al., 2000, Sorenmo, 2003, Ezerskyte et al., 2011). By respect to age-related incidence, our data are very Volume IV, Number 5, 2014 Animal studies & Veterinary medicine ...