Mammary Osteosarcoma with Neoplastic Emboli in Cerebellum
Background: The mammary neoplasms are highly frequent in female dogs. It is characterized by the proliferation of epithelial or mesenchymal cells. The mammary osteosarcoma is a example of the proliferation of the last group and its main feature is production of osteoid matrix production and areas of mature bone tissue formation. Metastases to the lungs and regional lymph nodes are frequent, however some other metastasis sites have been reported. The aim of this study is to report a mammary osteosarcoma in a mixed-breed female dog of 12 years old with multiple metastases and neoplastic emboli to the central nervous system.
Case: The animal was brought to the Veterinary Hospital of the Uberlândia Federal University (HV/UFU) with the complaint of increase in the volume of the mammary glands. The cytopathological exams was performed in the mass that measured 15 cm of diameter and covering a large region of the mammary gland, from the right cranial thoracic to the right cranial abdominal mammary gland. The cytological diagnostic was inconclusive because of the lack of material for diagnosis. Therefore, total unilateral mastectomy was performed for histopathology analysis. The material was then sent to the Animal Pathology Laboratory of the HV/UFU where routine processing was performed. The microscopy showed proliferation of mesenchymal cells arranged in bundles with intense pleomorfism and producing osteoid matrix, leading to the diagnosis of mammary osteosarcoma. Around 15 days after the diagnostic the animal died and was sent the Animal Pathology Laboratory of the HV/UFU for necropsy. During the external exam there was a mass at the same site of the primary mass previously extracted. Besides it, there were masses affecting lungs, intestine and kidneys. The histopathological exam showed sites of metastasis of osteosarcoma in the organs described, as well as neoplastic emboli in the cerebellum, fortifying the metastatic potential of this neoplasm.
Discussion: Mammary osteosarcomas are classified mainly based on the appearance of osteoid matrix produced by osteoblast-like cells or presence of mature bone formation. In the mammary gland it is important to highlight that the neoplasia should not show tubular epithelial cells proliferation, otherwise a better classification of the disease would be carcinosarcoma. The origin of the osteoid cells in this neoplasia is still in discussion. Some authors believe that, like in other regions as thyroid gland, the osseous metaplasia in this region can lead to malignant differentiation of the metaplastic tissue originating the osteosarcoma. The gross appearance, age and breed of the animal are frequently associated with this neoplasia, and it is in agreement of other cases reported previously by different authors. Although metastases are common in this neoplasia, the involvement of the central nervous system is rare and the reports of this condition are usually associated to osteosarcoma of the appendicular skeleton origin. Even though the dog did not show any neurological clinical sign or macroscopic lesion in the central nervous system, this report highlights the importance of complementing these exams with histopathology. In this case we show a microscopic finding made only with an accurate exam of serial transversal cuts of the brain. In conclusion, more descriptive studies of mammary osteosarcoma must be made to a better interpretation of this neoplasm behavior.
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