Dr. Tilaye DemissieMesfin, Mathewos2018-10-182023-11-302018-10-182023-11-302018-06http://etd.aau.edu.et/handle/123456789/12889A thesis submitted to the College of Veterinary Medicine and Agriculture of Addis Ababa University in partial fulfillment of the requirements for the degree of Master of Science in Veterinary PathologyTumors are one of the disorders that affect domestic animals. The present study was conducted from October, 2017 to May 2018 with the objectives of determining the types and frequencies of tumors of domestic animals based on cytological and pathological characteristics. A cross-sectional study with purposive sampling of animals with swelling or masses was conducted for evaluation of masses by gross examination, cytology and histopathology. A total of sixty neoplastic swelling were identified. Based on cellular origin, the overall frequencies of tumors were found to be 46.7% epithelial, 36.7% unclassified, 13.3% mesenchymal and 3.3% were round cell tumors. Gross lesions observed include firm consistency, cauliflower like lesions, nodular mass, ulcerated, inflamed and haemorrhagic surfaces, pediculate, necrosis, and lobulated mass with irregular margins. Cytologically, most of the epithelial cell tumor and equine sarcoid revealed clusters of cells with different arrangements, deep nuclear chromatin, anisocytosis and anisokaryosis. Where as, all tumors of mesenchymal origin including fibropapilloma showed pleomorphic spindle cells. Mast cell tumors was characterized by its cytoplasmic granules and transmissible venereal tumors by clear punctuate intracytoplasmic vacuoles, cell shape and prominent central nucleoli. Histopathologically, equine sarcoid and papillomatosis were characterized by dermal keratinocytes proliferation, long rete pegs that extend deep into the dermis. Ocular squamous cell carcinoma was characterized by keratin tonofilaments and keratin pearls while, leiomyoma, cutaneous fibrosarcoma, basal cell carcinoma and hemangiopericytomas were characterized plump smooth muscle-like cells, herring bone pattern, cluster of neoplastic basal cells and perivascular whorls of pericyte nuclei, in the respective order. Mammary tumors were characterized by severe cellular and nuclear pleomorphism, and highly infiltrative. Sertoli cell tumor, fibrothecoma, cutaneous mast cell tumor, transmissible venereal tumor and malignant fibrous histiocytoma were chracterized by sheets of sertoli cells, spindle cells with plump thecoma cells, granulated mast cells, round cells with vesicular nuclei and pleomorphic histiocytic cells, respectively. Based on the result it could be concluded that domestic animals were widely suffering from tumors of different origin. Thus, studies involving large sample size, and wider diagnostic tools should be conducted. Key words: Cytology, Domestic animals, Ethiopia, Histopathology, TumorsenCytologDomestic animalsHistopathologyThesis