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OSTEOSARCOMA IN GREYHOUNDS

"Charming" 3/26/92-11/10/04                       "Roxanne" 6/5/93-2/11/05
Osteosarcoma of Humerus                      Osteosarcoma of Distal Radius

C. GUILLERMO COUTO, DVM, Dip. ACVIM

Department of Veterinary Clinical Sciences
College of Veterinary Medicine,
The Ohio State University, Columbus, OH 43210

Primary bone tumors (neoplasms) are common in dogs. Most primary bone tumors in dogs are malignant, in that they usually cause death as a result of local infiltration (e.g., pathologic fractures or extreme pain leading to euthanasia) or dissemination (e.g., pulmonary metastases in osteosarcoma-OSA). Neoplasms that metastasize (spread) to the bone are extremely rare in dogs; some malignant tumors that occasionally metastasize to bones are transitional cell carcinoma of the bladder, osteosarcoma in other bone/s, hemangiosarcoma, mammary adenocarcinoma, and prostatic adenocarcinoma.

Osteosarcomas are the most common primary bone tumor in dogs, and the most common tumor in Greyhounds in the United Kingdom, where it accounted for 50% of all tumors, and for 22% of the deaths in the breed (www.gurk.demon.co.uk /ghsurvey). Cancer in general (44%), and OSA in particular (22%) were the leading cause of death in the breed. At the University of Florida, 10% of all dogs with OSA were Greyhounds, and the risk of developing OSA was higher for Greyhounds than for any other breeds.

OSAs can affect either the appendicular (e.g.; legs) or axial (e.g.; spine, skull) skeletons, and occur primarily in large (and giant)–breed, middle age–to-older dogs. Preferential locations for OSA include the distal radius, proximal humerus, and distal femur, although they can occur in any bone or location; they are more common in dogs over the age of 6 or 7.

Their biologic behavior is characterized by aggressive local infiltration of the surrounding tissues and rapid dissemination through the bloodstream (usually to the lungs). Although when first discovered, most dogs with OSA have “clean” thoracic radiographs (chest X-rays), there are usually tumor cells present in the lungs, but the masses are too small to be seen in routine radiographs.

Clinical Signs (“Symptoms”)

OSAs occur predominantly in the ends of the distal radius (wrist), distal femur (knee), and proximal humerus (shoulder)(“TOWARDS THE KNEE AND AWAY FROM THE ELBOW"), although other areas can also be affected. In contrast with other breeds, where dogs with OSA typically develop bone swelling and/or limping, Greyhounds frequently develop a spontaneous pathological fracture (i.e.; the bone breaks or fractures without any trauma). orthopedic problem, and thus delaying diagnosis y also occur.

Osteosarcoma of distal radius in front leg

Diagnosis

Destructive and proliferative bone changes in dogs with OSA
(see above photos for corresponding presentation
at time of examination)

A less invasive alternative to a biopsy is fine-needle aspiration (FNA) of the affected area; in this procedure, which does not require general anesthesia, as the biopsy, a small hypodermic needle is inserted into the lesion, and a drop of tissue is microscopically evaluated by a Clinical Pathologist.

If the cytology is not diagnostic, and you are still debating whether to go ahead with the limb amputation, a core biopsy of the affected area should be obtained. For this, your veterinarian will use a large bore needle with your hound under general anesthesia. The diagnostic yield of this procedure is quite high (approximately 70% to 75%), but because Greyhounds have very thin bones, the bone may fracture (break) around the area of the biopsy. y

As long as you are aware of the biologic behavior of the tumor and the clinical and radiographic features of the lesion are compatible with OSA, the limb can be amputated in the absence of a biopsy. The amputated leg (or representative samples) should always be submitted for histopathologic studies.

Treatment and Prognosis

The treatment of choice for dogs with OSA is amputation of the affected limb, with adjuvant chemotherapy (another “bad word”-see below). The median (average) survival time of dogs with appendicular OSA treated with amputation alone is approximately 4 months, whereas in dogs treated with amputation and chemotherapy it is approximately 1 year.

An issue your veterinarian should be familiar with is the fact that amputation in Greyhounds frequently results in severe postoperative bleeding around the surgical site, leading to subcutaneous blood accumulation in the other limbs, ventral thorax, and ventral abdomen; your veterinarian should have access to plasma or other blood products before the surgery. Alternatively, you can ask your vet to refer you to a specialist (board-certified surgeon or oncologist).

A novel surgical approach for dogs with distal radial (wrist) OSA consists of sparing the affected limb. Instead of amputation, the affected bone is resected and an allograft from a cadaver is used to replace the neoplastic bone; novel biomaterials are also currently being investigated for this purpose. The dogs are also treated with intravenous chemotherapy and, in general, have almost normal limb function. The main complication is the development of osteomyelitis (infection) in the allograft; if that occurs, the limb frequently needs to be amputated. Survival times in dogs treated with limb-sparing procedures are comparable to those in those that undergo amputation plus chemotherapy, with the added benefit to the owners of having a four-legged pet.

The chemotherapeutic agents typically used for Greyhounds with OSA are cisplatin, carboplatin, or doxorubin. The treatment results are almost identical for the 3 drugs; because cisplatin has to be given as an IV infusion, most oncologists are no longer using it. So, basically, we are considering one of 2 conventional treatments: 5 doses of doxorubicin (Adriamycin) at 2-week intervals, or 4 doses of carboplatin (Paraplatin) at 3-week intervals. Doxorubicin is relatively inexpensive (a little bit over $120/dose for the cost of the drug), whereas carboplatin is one of the most expensive chemo drugs (approximately $40/kg of body weight, or an average of $1,000/dose). However, carboplatin causes almost no side effects, whereas approximately 20% of dogs receiving doxorubicin have mild side effects, such as poor appetite, diarrhea, etc; also, dogs with some types of heart disease cannot receive doxorubicin. These side effects are minimal when compared with those in people on chemo. And, oh, by the way, dogs on chemo don’t lose their hair. For the average dog on chemo, there is no difference in the quality of life when compared to that before chemo. ends with

If amputation is not an option, local radiotherapy plus chemo may be of some benefit. However, in our limited experience, most dogs are eventually euthanized within 3 to 4 months of the initial diagnosis because of the development of pathological fractures (i.e., after radiotherapy the tumor is not as painful; therefore the dog regains normal use of the limb and fractures the area), osteomyelitis, or metastatic lesions.

Pain control is essential in dogs where surgery is not an option; we have used either NSAIDs (carprofen, deracoxib, meloxicam) at recommended doses, or bisphosphonates such as alendronate (Fosamax). Drugs such as tramadol (Ultram) are also beneficial.

© C. Guillermo Couto, DVM
couto.1@osu.edu
http://www.vet.ohio-state.edu/1872.htm
This article may not be reproduced or published
without express consent of the author
couto.1@osu.edu

GreytHealth thanks Dr. Couto for his generosity in contributing this article, which will be an invaluable resource for owners of Greyhounds (and indeed all canine breeds) faced with this devastating diagnosis. The information Dr. Couto has provided will hopefully assist our readers in better understanding the diagnosis, treatment options, and prognosis of osteosarcoma. If you are concerned that your Greyhound may be displaying some of the signs of osteosarcoma described by Dr. Couto, PLEASE SEEK VETERINARY CARE IMMEDIATELY!

by Suzanne Stack, DVM

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