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1. Chemotherapy: systemic cisplatin, carboplatin, doxorubicin, or combination therapy after the surgical treatment.
2. Several other adjuvant drug delivery systems that are under current investigation. Examples are: (a) the implantation of a platinum polymer (OPLA-Pt) that releases slowly relatively low concentrations of platinum into the circulation but reaches up to 30-fold high concentrations locally and (b) the combination of immune stimulant lipospheres with chemotherapeutics.
3. Resection of solitary metastatic pulmonary nodes (metastasectomy). This is performed either with nodulectomy or complete or partial lo- bectomy. The criteria that increase the probability of a longer survival period include
• Complete remission of the primary tumour, preferentially >300 days
• One or two metastatic nodules visible on radiographic examination
• No other signs for metastatic disease elsewhere
4. Pre-operative radiation of the tumour. Radiation therapy can cause considerable necrosis of the OS and is used in an effort to downstage the tumour and improve local disease control following surgical removal of the tumour.
OS needs to be differentially diagnosed from other canine primary bone tumours.
Chondrosarcoma is considered to have a low metastatic potential but up to 25% metastatic rates are reported. Chondrosarcoma develops most commonly
in large- and medium-breed dogs. Aggressive
surgical resection often results in very long surgical tumour control with low- and intermediate-grade tumours, i.e. 2.7 and 6 years, respectively. High-grade chondrosarcoma carries a poorer prognosis with 0.9-year survival time. There is no reliable adjuvant chemotherapeutic agent. Differential diagnosis is based (a) on the location of the tumour: the proximal tibia is the most common localization for chondrosarcoma, whereas the distal radius is the most common one for OS and
(b) on histological examination of the entire tumour after complete surgical excision.
Primary hemangiosarcoma is a rare bone tumour.
It is highly metastatic and virtually all dogs will develop metastasis within 6 months of diagnosis. The metastasis is wide spread and makes it difficult to determine which the primary tumour is. The predominant radiographic sign of hemangiosarcoma is lysis of the bone. It has a very poor prognosis, i.e., less than 10% 1-year survival if the tumour can be completely excised.
Fibrosarcoma is a rare primary bone tumour with
low metastatic potential in low and intermediate-
grade tumours and up to 50% metastatic rate in high- grade tumours. Complete resection of the tumour
that is clinically confined to the primary site can be curable. On a histological level, it is very difficult to differentially diagnose fibrosarcoma and fibroblastic osteosarcoma, especially from relatively small tissue samples. It is therefore, crucial to re-evaluate the tumour histopathologically after complete surgical resection.
An Urban Experience
Osteomas are benign tumours of the bone. The differential diagnosis is based on the fact that (a) the tumours are radiographically well defined and radiodense and (b) the tumour location is not painful on palpation. Surgical excision of the tumour is curable.
Multiple cartilaginous exostosis is considered a developmental hereditable disorder of growing dogs. They stop growing as soon as dogs reach skeletal maturity. Occasionally, malignant transformations occur. The differential diagnosis is based on (a) the age of the patient, (b) the non- or moderate painful palpable mass at the metaphyseal are of the long bones, (c) the benign radiographic appearance with a trabecular pattern. Surgical excision is advised only when clinical signs do not decline after skeletal maturity.
Bone cysts are benign lesions of the bone. The differential diagnosis is based on (a) the young age of the animal, (b) the radiographically multilobular, sharply defined radiolucent defects in the medullary canal of the long bones. It needs to be confirmed with histological examination since it may resemble radiographically a highly resorptive OS.
Bacterial and fungal osteomyelitis. Bacterial osteomyelitis is usually associated with a history of a penetrating trauma, like dog bites and open fractures. Fungal osteomyelitis is related to geographic location
or history of travel to endemic fungal areas. Particulary fungal osteomyelitis should be considered due to the fact that it is preferably monostotic and located in the metaphyseal are of long bones. The most common fungal organisms affecting bone are Coccidioides immitis and Blastomyces dermatitis. Differential diagnosis is based upon (a) the history and signalment of the patient, (b) clinical presentation (febrile, general illness, possible lung infiltrates due to pulmonary infection), (c) serology, and (d) histologic examination and (fungal) culture
*Manuscript is adapted from previous version written by Marianna Tryfonidou- van Megen, Diplomate ECVS.

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