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The Daily Vet by petMD

The Daily Vet is a blog featuring veterinarians from all walks of life. Every week they will tackle entertaining, interesting, and sometimes difficult topics in the world of animal medicine – all in the hopes that their unique insights and personal experiences will help you to understand your pets.

Duffy’s owners noted that he was limping on his right front leg a few weeks ago. They didn’t give it much consideration at the time. It wasn’t unusual for this handsome and active 9-year-old Golden retriever to tweak a muscle once in a while, and after a few days of rest and prescription anti-inflammatory medication, Duffy was feeling much better.

The lameness returned about ten days later, and this time they noticed a swelling above Duffy’s carpus (wrist) on the same limb. They recognized this wasn’t just a sore muscle and they made an appointment with his primary veterinarian the next day.

Duffy’s vet performed radiographs (X-rays) of the swelling over his carpus. The images revealed near complete destruction of the distal (lowest) part of the radius (weight-bearing bone of the forelimb) with a significant amount of swelling and also some new bone formation. All of these signs unfortunately pointed towards the high likelihood that Duffy had bone cancer. Duffy’s doctor recommended they come talk to me about different options available for obtaining a definitive diagnosis and also to learn about some potential treatment options.

I met Duffy and his worried owners soon after. I agreed with Duffy’s vet and discussed the likelihood that he had a specific type of bone cancer called osteosarcoma. This very aggressive tumor causes significant pain for affected dogs, and is also highly metastatic, meaning there was a high chance the tumor cells had already spread to distant sites in Duffy’s body. The most common sites of spread would be the lungs and other bones.

I talked with Duffy’s owners about tests we could perform to be certain of my concern and also how we could look for any spread of his cancer. The “gold-standard” test for diagnosing bone cancer in dogs is a biopsy, where small pieces of the affected bone are removed with a surgical procedure under general anesthesia.

Although a biopsy is likely to provide an accurate diagnosis, there are some downsides to the procedure. The turn around time for biopsy samples can be as long as a week or more, and during that time pets are still painful, and there is a risk (albeit low) for causing a fracture of an already weakened bone. There is also a small risk of infection and bleeding, and if not planned correctly, seeding tumor cells into the surrounding connective tissue.

For dogs with suspected bone cancer, I typically recommend we start with an ultrasound guided fine needle aspirate of the lesion itself. This is a relatively straightforward procedure that is performed under light sedation. A medium-sized needle is inserted into the affected bone and cells can be extracted and evaluated under a microscope by a trained cytopathologist.  The major pro of this test is the rapid turn around time (within 24-48 hours in most cases), and the risk of inducing a fracture is minimal.

The fine needle aspirate test is very good for obtaining a diagnosis of “cancer vs. not cancer.” Results typically indicate either sarcoma (cancer) or reactive bone (no obvious cancer). Sarcomas are tumors of connective tissue, and bone is an example of one of many types of connective tissue in the body.

When it comes to bone sarcomas, there are several types we commonly see within bones. As stated above, osteosarcoma would be the most common type, followed by chondrosarcoma, fibrosarcoma, and hemangiosarcoma. Other primary bone tumors include histiocytic sarcoma and multilobular osteochondrosarcoma.

The reason an aspirate lacks the specificity to determine the subtype of sarcoma is because with this procedure we are just extracting individual cells, whereas a biopsy sample will obtain not only tumor cells, but other elements of the bone itself that help a pathologist determine the exact nature of the tumor.

If an aspirate sample returns positive for sarcoma, an additional test (alkaline phosphatase stain) can be performed to rule in or rule out osteosarcoma. I urge owners to start with an aspirate first as I find it the most rapid way to obtain a diagnosis with minimal risk to the patient.

I discussed this with Duffy’s owners and they elected to move forward with the radiographs of his lungs and the fine needle aspirate procedure. As expected, Duffy handled the procedure perfectly, with no complications. We added some stronger pain medications to his at home anti-inflammatory treatment and he left that day still limping, but carefree and happy, not understanding his owners’ worry at all.

Two days later, late in the evening after finishing my appointments, I sat down to call Duffy’s owners. On a conference call with both owners eagerly awaiting my words, I sadly relayed that the test results confirmed our suspicions: Duffy had osteosarcoma. 

I’m not often the one breaking the news of a diagnosis of cancer to owners, but when I do I’ve noticed there are several typical reactions. Some owners will become angry and lash out while others are too upset to speak. Duffy’s owners fell into the “strong but silent” type, not really showing much emotion, stoically listening to my words with a bit of detachment and hint of skepticism. They asked what the next step would be, and I told them I recommended they schedule an amputation of Duffy’s affected limb as soon as possible.

The subtle short intake of breath by both owners was barely audible through the phone, yet I immediately knew its significance. In it, I detected the fear of the prospect of surgery and what it would mean for Duffy to live the remainder of his life as a three-legged dog. I’ve had this discussion with owners numerous times before, and I knew I was about to embark on a lengthy and emotionally driven conversation.

I literally kicked off my heels and put my feet up on my desk and stated, “Try not to panic. Let me tell you what you can expect…”

Next week, stay tuned to learn about what Duffy’s owners decided and learn more about therapeutic options and the prognosis for a dog with osteosarcoma.

Dr. Joanne Intile

Image: Thinkstock

Comments  2

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  • 07/24/2013 06:57pm

    The biggest fear of waiting for a bone biopsy, in my opinion, is that gives possible cancer an extra week to spread.

    How much can be found on a radiograph? Obviously you won't see single mutant cells, but how early could cancer be found if it has metastasized (that may be treatable)?

    I'm anxious to hear what was decided for Duffy because it's my understanding that losing one limb usually isn't that traumatic for a critter. (It's much more traumatic for the humans.) Fingers crossed that Part 2 of the story has a happy ending.

  • 07/29/2013 09:41am

    Hi

    To answer your question about radiographs and being able to detect metastases from bone cancer; we typically use this imaging modality to look for spread to the lungs. Tumors in the lungs need to be of a certain size to show up on plain films. They probably need to be anywhere from 6-7 mm or larger. I was taught during my residency, tumors that large already contain a billion cancer cells in them. So if you see spread to the lungs on the films, that's the main reason it's already "too late". Tumors smaller than this will not show up on an x-ray. Radiographs are a good "jumping off" test as if obvious spread is detected, it will often dictate further recommendations. If you can stay tuned for the remaining series of articles, I'll answer your question more specifically (hopefully) and address the issue of the three-legged dog lifestyle :)

    Joanne

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