Osteosarcoma

Osteosarcoma (OSA) is the most common primary bone tumor in dogs and cats, with a higher incidence in dogs, particularly middle-aged to older large and giant breeds. Appendicular OSA predominantly affects the metaphyseal regions of long bones, with the distal radius and proximal humerus being the most common sites. Risk factors include genetic mutations, skeletal implants, chronic osteomyelitis, and exposure to ionizing radiation. OSA is characterized by the production of osteoid and exhibits various histologic subtypes, though these do not significantly impact prognosis. Clinically, OSA presents as a proliferative or lytic bone lesion, often accompanied by lameness and, in some cases, pathologic fractures. Metastases, primarily to the lungs, are rare at initial diagnosis but may present with nonspecific signs such as weight loss. Radiographic evaluation is typically sufficient for diagnosis, with characteristic features including aggressive lysis, cortical destruction, and periosteal reaction. Treatment involves surgical excision, often limb amputation, which provides pain relief and improved survival times but is not curative alone. Chemotherapy is used adjunctively to extend survival times, particularly when surgery is not feasible.