of osteosarcoma of the distal femur in a dog risk factors osteosarcoma is the most common bone tumor in dogs and typically affects middle-aged large and giant breed dogs such as irish wolfhounds, greyhounds, german shepherds, rottweilers, mountain breeds (great pyrenees, st. bernard, leonberger, newfoundland), doberman pinschers and great danes. it has a 10-fold greater incidence in dogs than humans. a hereditary base has been shown in st. bernard dogs. spayed/neutered dogs have twice the risk of intact ones to develop osteosarcoma. infestation with the parasite spirocerca lupi can cause osteosarcoma of the esophagus. clinical presentation the most commonly affected bones are the proximal humerus, the distal radius, the distal femur, and the tibia, following the basic premise "far from the elbow, close to the knee". other sites include the ribs, the mandible, the spine, and the pelvis. rarely, osteosarcoma may arise from soft tissues (extraskeletal osteosarcoma). metastasis of tumors involving the limb bones is very common, usually to the lungs. the tumor causes a great deal of pain, and can even lead to fracture of the affected bone. as with human osteosarcoma, bone biopsy is the definitive method to reach a final diagnosis. osteosarcoma should be differentiated from other bone tumours and a range of other lesions, such as osteomyelitis. differential diagnosis of the osteosarcoma of the skull in particular includes, among others, chondrosarcoma and the multilobular tumour of bone. treatment and prognosis amputation is the initial treatment, although this alone will not prevent metastasis. chemotherapy combined with amputation improves the survival time, but most dogs still die within a year. surgical techniques designed to save the leg (limb-sparing procedures) do not improve the prognosis. some current studies indicate osteoclast inhibitors such as alendronate and pamidronate may have beneficial effects on the quality of life by reducing osteolysis, thus reducing the degree of pain, as well as the risk of pathological fractures. molecular alterations canine osteosarcoma shows similar patterns of molecular somatic alterations to the human disease. both are characterized by genetic instability and karyotypic complexity and genes that are recurrently altered include tp53, rb1, pten, myc, pik3ca. in contrast, mutations in the histone methyltransferase gene setd2 are rare in human osteosarcoma, but have been identified in 21 % of canine tumors. cats osteosarcoma is also the most common bone tumor in cats, although not as frequently encountered, and most typically affect the rear legs. the cancer is generally less aggressive in cats than in dogs, so amputation alone can lead to a significant survival time in many affected cats, though post-amputation chemotherapy is recommended when a high grade is confirmed on histopathology. dinosaurs a 2020 study was able to demonstrate via radiographic and histological analysis along with comparisons with osteosarcoma in humans that a centrosaurus from the cretaceous period had developed osteosarcoma in its fibula.