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).
If
your Greyhound has an OSA, he/she will likely have a painful swelling in the
affected area. The pain and swelling can come up suddenly, leading to the
presumptive diagnosis of an unrelated orthopedic problem, and thus delaying
diagnosis and definitive treatment for the neoplasm. As mentioned above, a
spontaneous fracture of the leg may also occur.
Osteosarcoma
of distal radius in front leg
(click on thumbnail views for full-size photo)
Diagnosis
Radiographs of the affected area usually reveal bone destruction and new bone formation; with very few exceptions (e.g.; bone infection or osteomyelitis, or coccidioidomycosis-a fungal infection prevalent in the Southwest), the radiographic appearance of bone cancer is very characteristic. As discussed above, chest X-rays (thoracic radiographs) should also be obtained.
Destructive
and proliferative bone changes in dogs with OSA
(see above photos for corresponding
presentation
at time of examination)
As
a general rule, a biopsy of the affected area should be obtained before you
decide on a specific treatment. If you and your veterinarian have already
decided that amputation (see below) is the initial treatment of choice for that
lesion, there is no need to do a pre-operative biopsy, since your veterinarian
will submit the appropriate tissues for histopathologic evaluation (biopsy)
after the surgery.
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.
When
you are facing the issue of whether to amputate your beloved dog’s leg or not,
there are no easy answers. Most owners are devastated by just thinking about
this procedure; the first question that comes to mind is: “are
we doing the right thing for him or her?”. Moreover, the “peer
pressure” (“You are so cruel by
putting him/her through that horrible procedure”) is enormous. As somebody
who has had Greyhounds for over 15 years, and who deals with amputees every week
(amputation is very common in veterinary cancer patients), I believe that
Greyhounds are among the best possible candidates for this procedure. As a
general rule, they are athletic, almost never overweight, and they have already
been “3-legged” by virtue of not using that leg due to pain. Although in
some dogs recovery may take as long as 2 weeks, they typically do great after
the surgery. My motto is “dogs come out
of the factory with 3 legs and a spare one”. Because pain is such an
important component of this disease, rapid pain relief is accomplished after the
surgery. 
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.
We
are currently investigating a novel approach to enhancing the effects of
chemotherapy in Greyhounds with OSA, by administering suramin, a drug that
increases sensitivity of the cancer cells to doxorubicin. Preliminary results
are encouraging, and the administration of suramin prior to doxorubicin does not
appear to increase the toxicity (side effects) of this chemotherapeutic agent.
If you are potentially interested in enrolling your dog in this clinical trial,
please contact Dr. Couto at couto.1@osu.edu
or visit the OSU Oncology Service website at www.vet.ohio-state.edu/docs/ClinSci/onco/index.htm.
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
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!