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J. Kirpensteijn1
1Hill’s Pet Nutrition, GPVA, Topeka, USA
Surgical treatment of appendicular bone tumours in the dog and cat
Jolle Kirpensteijn, DVM, PhD. Diplomate ACVS & ECVS
Chief Professional Relations Officer, Hill’s Pet Nutrition, Topeka, Kansas, USA.
Osteosarcoma (OS) is the most common bone tumour in the canine patient; it accounts for more than 85% of the malignancies originating in the skeleton. It is
a disease of the middle-aged large and giant breed dog and older cat. Predictive factors are increasing weight and more specifically increasing height in dogs. The breeds more at risk are St Bernard, Great Dane, Irish Setter, Doberman pincher, Rottweiler, German Shepherd, and Golden Retrievers. No specific breed information is available for cats
Canine bone tumours
75% of the OS occurs at the appendicular skeleton. The most common primary site is the metaphyseal region of the long bones. The predilection sites are “far from the elbow” and “near the knee joint”, i.e., proximal humerus and distal radius, and distal femur and proximal tibia, respectively. The remaining 25% of the OS occurs at the axial skeleton. The most common primary sites are: 27% mandible, 22% maxilla, 15% spine, 14% cranium, 10% ribs, 9% nasal cavity or sinuses, and 6% pelvis. Extra- skeletal OS is rare.
The aetiology of OS is largely unknown. Suspected physical factors include repetitive micro-trauma, metallic implants used for fracture repair, and radiation therapy. There is growing evidence that there may be molecular and genetic factors implicated in OS tumourigenesis. Gene mutations of retinoblastoma (Rb), p53, and c-Met have been suggested to increase the susceptibility to develop OS. Furthermore, growth factors, including growth hormone, insulin like growth factor 1, hepatocyte growth factor, and angiogenic factors have also been suggested to contribute to the malignancy of OS.
The clinical presentation of appendicular OS is a history of lameness and swelling at the primary site. There may be history of mild trauma prior to the onset of lameness. Acute and severe lameness is seen in case
of a pathologic fracture. The clinical presentation of axial OS is dependent upon the location of OS. Respiratory signs associated with clinical evidence of pulmonary metastasis are rare; additionally, less than 15% of the dogs will have radiographic visible pulmonary metastasis. Metastasis commonly occurs, although at presentation
it is often sub-clinical. Metastasis occurs through
the haematogenous route. Metastasis may also be encountered in the regional lymph nodes, however. A more sensitive detection technique than radiographs of pulmonary metastases is computer tomography.
Diagnosis is based upon
(a) full clinical, orthopaedic and neurological examination
(b) radiography: evaluation of the primary site and the thorax. Common radiographic findings are: lysis
of the cortex, soft tissue swelling, and new bone formation. The tumour invades the periosteum, lifts it up and new bone is laid down. The latter results in a triangular appearing deposition of bone on the cortex at the periphery of the lesion, the Codman’s triangle.
(c) computer tomography of the thorax for the evaluation of pulmonary metastasis
(d) cytology of the primary site and of enlarged lymph nodes. Typically osteoblasts are encountered in the case of OS.
(e) tissue biopsy. OS is a malignant mesenchymal tumour; the tumour cells are primitive osteoblasts and produce osteoid. The latter is used as
criteria for the histological diagnosis of OS. A
small biopsy sample before surgery may help to confirm a preliminary diagnosis. Misdiagnosis, however, including chondrosarcoma, fibrosarcoma, hemangiosarcoma or reactive bone, is relatively common due to the mixed histologic appearance
of the tumour. Therefore, it is essential that the diagnosis OS is confirmed with histologic evaluation of the entire tumour after definitive excision.
(f) blood examination for the general clinical work up of the patient. Elevated bone alkaline phosphatase has been correlated with a poorer prognosis of appendicular OS.
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