Cytological and Histopathological Correlation of Feline Giant Cell-Rich Osteosarcoma

Background: Primary bone tumours are uncommon and poorly reported in cats but osteosarcoma (OSA) is the most frequent, mostly in elderly animals. Giant cell-rich OSA is considered rare in the literature representing 3% of all OSA in humans. The mitotic index seems to have a significant effect on the survival time of cats affected by this neoplasm as well as the tumour histopathological grade. The objective of this study was to report the cytological and histopathological findings of a giant cell rich OSA in a 4-year old cat with persistent feline leukemia virus (FeLV) antigenaemia.Case: A 4-year-old male neutered cat was referred with a history of persistent FeLV viraemia and pelvic limb lameness with a firm swelling. Previous radiographs of the affected limb revealed bone lysis in the third and fourth metatarsals and increased soft tissue radiopacity in the tarsal region. The referral veterinary assumed it to be osteomyelitis and initiated clinical treatment with antibiotic and anti-inflammatory. The cat was referred after there was no response to medical treatment. The cat was presented with a 5cm diameter ulcerated mass, with putrid odor in the pelvic limb. Complementary exams were performed, and abnormalities were found, including increased urea, creatinine, calcium and potassium, and decreased sodium and phosphorus. A new radiograph showed exuberant bone proliferation, with increased radiopacity involving tarsal, metatarsal, distal third of tarsal I and II, and distal diaphysis of metatarsal V, without compromising the metaphyseal region of distal diaphysis of metatarsal IV. Chest radiographs and abdominal ultrasound were unremarkable. Fine-needle aspiration was performed for cytological analysis, which reavealed a moderate amount of pleomorphic mesenchymal cells with moderate adhesion, cytoplasm with a format ranging from fusiform to stellate, pronounced anisocytosis and cellular pleomorphism, and elevated nucleus:cytoplasm ratio. Nucleus was oval and presented loose chromatin, single to double large and evident nucleolus, frequent karyomegaly, along with marked anisocariosis and nuclear pleomorphism. Multinucleated giant cells were and there was a single mitotic figure in 12 high power fields (0.196 mm2 FN20/400x). Therefore, it was suggestive of malignant mesenchymal neoplasia with possibility of OSA, fibrosarcoma oe undifferentiated sarcoma. Limb amputation with femoral disarticulation was performed uneventfully. The material was conserved in 10%