Mediastinal extraskeletal osteosarcoma in a canine with pulmonary and cerebral metastasis

ABSTRACT

Background: Extraskeletal osteosarcoma (EOS), a rare variant of osteosarcoma (OS), is a malignant neoplasm that develops insoft tissues without primary bone involvement. This study aims to describe a case of EOS with a mediastinal location in a canine.Case A 10-year-old male Uruguayan Cimarron dog, was presented to the Laboratório Regional de Diagnóstico, Faculdadede Veterinária, Universidade Federal de Pelotas (LRD/FV/UFPel) for necropsy. The dog had a history of submandibularswelling, progressive hind limb paralysis, muscle atrophy, and breathing difficulties. During necropsy, in the thoracic cavity,approximately 900 mL of serosanguinous exudate and a reddish-brown, bossed mediastinal mass measuring 15.0 cm in thelongest axis were also noted. The lung exhibited multifocal to coalescent, white, firm nodules extending from the pleurato the parenchyma and measuring up to 4.5 cm in diameter. In the parietal and occipital region of the brain, a matte winemass measuring 2.3 cm in the longest axis was observed. Fragments of the neoplastic mass, organs of the abdominal andthoracic cavities, and the brain were harvested and fixed in 10% buffered formalin. After 48 h, the samples were routinelyprocessed, incorporated in paraffin, cut into 3 µm-thick sections, and stained using Hematoxylin and Eosin (HE). Selectedsections of the neoplasm, the lung, and the brain were subjected to Von Kossa staining and immunohistochemical (IHC)analysis. For IHC, primary anti-cytokeratin monoclonal antibodies (clone AE1 / AE3, BioCare Medical) at a 1100 dilution, vimentin (clone V9, BioCare Medical) at a 1100 dilution, S100 Protein (clone 15E2E2, BioCare Medical) at a 1100dilution, and Ki67 (SP6 clone, BioCare Medical) at a 150 dilution were used. Immunostaining ...