As I discussed in the previous blog, the first sign of osteosarcoma (OSA) that a pet Guardian sees is usually limping, or refusing to put weight on the leg involved. This is because bone tumors hurt, especially when the bone bears weight — so your dog will be lame or will limp. You may see swelling in the area of the tumor, but it can be hard to see the mass, especially the ones higher on the leg or in dogs with a lot of fur.
Am I suggesting that every dog that suddenly limps has OSA? Clearly not, but if you have an at-risk dog (the large or giant breeds, including Great Danes, Saint Bernards, Irish Setters, Rottweilers, German Shepherds, Golden Retrievers, and Doberman Pinschers*), in the age-range risk (7 to 9 years of age, also 1.5 to 2 years of age), see your vet promptly. If your dog does not respond to pain medications and rest within a week, be sure to get x-rays.
(*In my last blog, I was reminded me to include Greyhounds. Thanks to my readers for pointing out I had forgotten to include this breed.)
If osteosarcoma is suspected, testing can get complicated (and expensive). Here are the tests that you will likely be asked to consider — and my advice about whether to do them or not.
Limb X-rays: Mandatory
Ideally, all large and giant breed dogs with persistent and significant pain and lameness should be evaluated with radiographs (X-rays). Be prepared to have multiple view X-rays of the affected bone, which means more than one X-ray, taken from different angles. There are classic “textbook” things your vet will look for. There are certain classic bone changes seen with these tumors, including their typical “sunburst” appearance. And there are also a spectrum of other changes that can be seen on X-rays, from mostly bone lysis (or destruction) to mostly new bone proliferation.
Biopsy before surgery: Not Mandatory
Normally, I recommend confirming a cancer diagnosis with cytology or biopsy before performing a cancer surgery, but I make an exception if OSA is suspected. This is based on patient’s age, breed, history, physical exam, tumor location in the bone, and X-rays. If all this point to OSA, I believe it is okay to proceed with amputation. (For amputation alternatives, check out the Guide).
Why proceed without a positive confirmation that the lesion is OSA? Because these aggressive bone lesions cannot be repaired, and they put the dog at risk for a serious and painful fracture. Amputation removes the destructive and painful process immediately. The leg will be submitted for biopsy at surgery, and this will allow tumor confirmation, and appropriate post-surgery treatments can be planned based on the biopsy report.
In other words, if OSA is highly suspected, you can stage the cancer (see below) and schedule a surgery, even if you do not yet have conclusive confirmation of cancer.
However, some owners are not certain if they want to treat OSA at all – they want to know for sure of the diagnosis before they decide how or whether to treat the cancer. In these cases, absolutely, a biopsy or bone aspirate should be performed first. (These tests are also discussed in the Guide.)
Chest X-rays (or CT scan): Mandatory
When you see bone lesions on X-rays, and OSA is suspected, chest X-rays should also be ordered and examined, ideally before amputation. That’s because OSA is agressive and tends to metastasize to the lungs. About ten percent of dogs with OSA have detectable spread to the lungs when they are diagnosed. Even though detectable spread to the lungs is uncommon, if you see it in your dog, the prognosis is significantly worse. In these cases, some guardians choose to reconsider the amputation and follow up chemotherapy and radiation treatments.
The simplest and most available imaging test is X-rays. Your vet should take three-view x-rays (not 2 views) of the chest cavity to look for lung metastasis. Chest CT scans are more accurate and can pick up these smaller lesions, but they aren’t available everywhere, require anesthesia, and are more expensive than X-rays.
Basic blood work and urine tests: Mandatory
Full blood panels, including a CBC and chemistry panel, should be run, and a urinalysis should also be performed.
Other Tests to Consider on a Case-by-CaseBasis
After lungs, the bones are the second most common site of metastasis, so if there are signs of pain or lameness in other areas of the body, they should be x-rayed to look for lesions. I do not typically recommend whole body x-rays, because of the added cost (it takes a lot of X-rays in a big dog to get this done) and overall low chance a dog (about 6%) has bone metastasis at diagnosis. If a dog is lame or painful in a second area, whole body x-rays or nuclear bone scan can be considered.
Regional lymph nodes should also be aspirated or biopsied to check for metastasis, even if they appear to be normal. Although lymph node spread is uncommon (occurring in less than 5% of dogs), its presence is a very negative prognostic factor; dogs with lymph node involvement live only two months, compared to eleven months. Knowing whether OSA has spread to the lymph nodes can help you make treatment decisions.
Metastasis to the abdominal organs is uncommon, so abdominal ultrasound is not routinely recommended. I will recommend one if there are blood work changes, if I think the bone tumor is a metastatic lesion and not the primary tumor, or for general health screening. Abdominal ultrasounds are not painful or invasive, and can be used to evaluate the dog’s overall state of health before embarking on extensive and expensive treatments.
In the next blog, we will discuss amputation. It’s a really hard decision for most owners. I would love your input. If you’d like to contribute to my poll, please check out my FB page. (Please scroll down to the Jan. 23rd post.)