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Osteosarcoma: What chemo? When? (Proceedings)

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Aug 01, 2010

Incidence and Risk Factors

Osteosarcoma (OSA) is the most common primary bone tumor in the dog (85% of skeletal malignancies). It is estimated to occur in over 8,000 dogs/year in the United States. OSA has bimodal age incidence peaks at 18-24 months and 7 years and occurs predominately in large to giant breed dogs in the appendicular skeleton at metaphyseal sites, whereas smaller breed dogs generally have their OSA in the axial skeleton. For appendicular OSA, the saying "Away from the elbow and close to the knee" is a good generalization; however, OSA can occur at sites such as distal tibia and others. In addition OSA is seen in the oral cavity (maxilla or mandibular), nasal cavity, ribs, digits and many other bony sites. The etiology of OSA is unknown but thought to be related to traumatic microfractures.

Pathology and Behavior

OSA is a malignant mesenchymal tumor of primitive bone cells. The presence of extracellular matrix production of osteoid helps differentiate OSA from other bone sarcomas such as chondrosarcoma, lymphosarcoma, Hemangiosarcoma, and others. There are multiple histologic sub-classifications (osteoblastic, fibroblastic, chondroblastic, telangiectatic, etc.) for OSA; however, sub-classifications do not presently appear to be prognostic. OSA causes bone lysis, production of bone, or both; pathological fractures can occur. Less than 5% of dogs present with radiographically detectable pulmonary metastasis whereas > 90% have micrometastases at presentation.

History and Clinical Signs

Most dogs with OSA present for lameness and/or swelling at the local site if appendicular in origin. For non-appendicular OSA, the history and clinical signs are dependant on the specific site of origin.

Diagnosis

Local radiographs document soft tissue swelling, bone lysis, production of bone, or a combination of both. The differential diagnosis for OSA includes: Primary or secondary bone tumor, myeloma, lymphoma, and osteomyelitis. The definitive diagnosis of OSA requires bone biopsy. While most biopsies of cancer aim for the periphery of a lesion, bone biopsies should be taken from the center of the lesion and multiple biopsies should be performed. In addition, a full physical examination with close palpation of local lymph nodes (aspirate & examine if enlarged) is also recommended. For additional staging, three view thoracic radiographs are strongly recommended. The utility of additional staging diagnostics such as bone survey radiographs and/or nuclear medicine bone scanning are somewhat controversial. A surgical staging system suggests most OSA are stage IIb (high-grade, extracompartmental and no gross metastasis).



Therapy: The median survival times reported for appendicular OSA are summarized in the table below.

History and Clinical Signs

Prognostic Factors 19-27

Better
     • No overt metastasis
     • tumor necrosis (neoadjuvant chemotherapy only)
     • ↑↑ Mandibular location

Worse
     • < 5 yr age
     • ↑↑ tumor size
     • Proximal humerus
           » 40 kg weight
     • ↑↑ ALP
     • ↑↑ grade

References

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2. Brodey RS, Riser WH (), Canine osteosarcoma. A clinicopathologic study of 194 cases, Clin.Orthop. 1969;62: 54-64

3. Mauldin GN, Matus RE, Withrow SJ et al. (), Canine osteosarcoma. Treatment by amputation versus amputation and adjuvant chemotherapy using doxorubicin and cisplatin, J Vet.Intern.Med. 1988;2: 177-180

4. McEntee MC, Page RL, Novotney CA et al. (), Palliative Radiotherapy for Canine Appendicular Osteosarcoma, Vet.Radiol.Ultrasound 1993;34: 367-370

5. Ramirez O, III, Dodge RK, Page RL et al. (), Palliative radiotherapy of appendicular osteosarcoma in 95 dogs, Vet.Radiol.Ultrasound 1999;40: 517-522

6. Green EM, Adams WM, Forrest LJ (), Four fraction palliative radiotherapy for osteosarcoma in 24 dogs, J Am Anim Hosp Assoc 2002;38: 445-451

7. Straw RC, Withrow SJ, Richter SL et al. (), Amputation and cisplatin for treatment of canine osteosarcoma, J.Vet.Intern.Med. 1991;5: 205-210

8. Kraegel SA, Madewell BR, Simonson E et al. (), Osteogenic sarcoma and cisplatin chemotherapy in dogs: 16 cases (1986-1989)., Journal of the American Veterinary Medical Assoc 1991;199(8): 1057-1066

9. Thompson JP, Fugent MJ (), Evaluation of survival times after limb amputation, with and without subsequent administration of cisplatin, for treatment of appendicular osteosarcoma in dogs: 30 cases (1979-1990), Journal of the American Veterinary Medical Assoc 1992;200: 531-533

10. Berg J, Weinstein MJ, Springfield DS et al. (), Results of surgery and doxorubicin chemotherapy in dogs with osteosarcoma, Journal of the American Veterinary Medical Association 1995;206: 1555-1560

11. Bergman PJ, MacEwen EG, Kurzman ID et al. (), Amputation and carboplatin for treatment of dogs with osteosarcoma: 48 cases (1991 to 1993),J Vet.Intern.Med. 1996;10: 76-81