Signs of Osteosarcoma (Bone Cancer) in Dogs
Osteosarcoma is a word derived from osteo, meaning bone, and sarcoma, meaning cancer. It's the cancer of the bones. It commonly strikes large dog breeds between middle age and the senior years, but has been known to affect dogs as young as two. Osteosarcoma is less common in small dog breeds. Breeds particularly predisposed to osteosarcoma include Saint Bernards, Rottweilers, Great Danes, Golden Retrievers, Irish setters, Doberman Pinschers, and Labrador Retrievers. On average it affects dogs in the 7-7.5 year range.
While it can affect basically any bone in the body, it typically affects the dog's legs (75-85% according to Mar Vista Vet). When a leg is affected, the condition is known as "appendicular osteosarcoma". Other predisposed areas include the ribs, vertebrae, and skull, yet bone cancer in these areas are rare. In this article, we will mostly tackle bone cancer of the limbs.
Link to pictures of dog legs affected by osteosarcoma
Signs of Osteosarcoma in Dogs
In osteosarcoma, the tumor originates from within the affected bone and destroys it from the inside out. The front limbs are most commonly affected, according to Vet Cancer Specialists. The cancer tends to form at or near the growth plates. The most common bones affected by osteosarcoma include, in order of preference:
1) distal radius
2) proximal humerus
3) distal ulna
4) distal femur
5) proximal tibia
6) distal tibia
7) diaphyseal ulna
As vets often say, osteosarcoma in dogs is mostly seen “near the knee” and “away from the elbow.” See picture for exact locations of these bones. Sadly, dogs with osteosarcoma do not show symptoms in the early stages, which is why this condition is always discovered late and it is one of the most devastating diseases for dog owners to endure.
- Progressive lameness
Owners often report limping in a forelimb or hindlimb without an evident cause and that does not get better with time. The lameness may wax and wane for some time, generally several weeks, but will not go away. Generally, the limping goes from intermittent to constant over the course of 1-3 months. It gets gradually worse as the cancer damages the bone and causes pain for the dog. However, some dogs may be quite stoic and not clearly manifest pain. The lameness is triggered by inflammation of the membrane that covers the outer surface of all bone, microfractures, or pathologic fractures. It's always a good idea to routinely observe your dog's gait so you can readily recognize signs of trouble.
Often, vets will try to treat the lameness symptomatically before running further tests. When the vet will do an x-ray, the affected bone may show signs of destruction (lysis) or abnormal growth, as seen in a typical sunburst pattern or Codman's triangle, signaling that the periosteum has been raised due to the tumor. In some cases, a biopsy of the bone may be needed to obtain a definitive diagnosis.
As the cancer expands, it will cause swelling in the affected limb or shoulder area (see pictures). This swelling is therefore due the expansion of tumor into the surrounding soft tissues.The swollen area may appear hot to the touch and the dog may exhibit pain as the area is handled. However, as mentioned, the pain may not be that noticeable in stoic dogs. It's always a good idea to routinely touch your dog's legs and get familiar with how the bones and skin feel. If you ever feel a lump by the bone, or individualize a swollen joint, see your vet. If you are not sure, you can always use the other leg for comparison.
The affected dog's bone typically become eroded and is replaced by tumorous bone which is friable and prone to fractures that do not heal. Typically, the dog owner reports that the dog was playing one minute, and yelping the next when the fracture occurred. The fracture in this case is known as "a pathologic fracture" since it affects tumorous bone. X-rays of the bones may show eroded bones, the typical sunburst pattern or Codman triangle, which provide a diagnosis.
- Difficulty breathing/Coughing
Sadly by the time the cancer is discovered, almost 90% of cases have already metastasized, according to the American Kennel Club's Canine Health Foundation. Microscopic metastasis is therefore often present at the time of diagnosis.The most common area of metastasis are the lungs.This explains why your vet will often do a chest x-ray (2 lateral views and a ventrodorsal one) as well to check if the cancer has spread. However, it appears that fewer than 10% of dogs show evidence of lung metastasis at the time of diagnosis, according to Vet Cancer Specialists. A CT scan of the lungs may be more effective than x-rays in identifying the initial small metastatic lesions. While metastasis to the lungs is the most common, other affected sites may be the liver, kidneys, amputation stump, and, nearby bones, even though rare.
- Behavior Changes
When dealing with cancer, the dog's immune system is put to test which results in lethargy and tiredness. The dog may weaken and appear less interested in food. Pain may cause walks or play to be too much for the dog. Affected dogs may sleep more, appear tired and pain may put a big toll in the dog's quality of life. The dog with bone cancer may also appear grumpy and may not want to be touched. Amputation may make the pain more bearable, but will not cure the disease.
Occurrence of Bone Cancer in Dog Front Legs (in order of preference)
Did you know?
About 10,000 new cases of osteosarcoma are diagnosed in dogs each year!
A Grim Future for my Rotties?
Owning two Rottweilers puppies, I looked forward to getting them vaccinated and giving them a great head start in life by playing it safe and preventing any major disease or weakness by feeding the highest quality foods and having routine check ups all their lives. However, once six months old, I asked the vet when the best age was to get them neutered and spayed and her answer was as early as possible. I trusted my vet, and vets in general because I always thought of all the years of education they undergo. So I had them altered immediately a week thereafter. Big mistake...
Little did I know back then that there were studies out there suggesting that large breed dogs spayed and neutered too early in life, were shown to be prone to osteosarcoma as they approached their middle to senior years! Actual studies have reported that chances of osteosarcoma decreased when Rotties were spayed and neutered once they were at least one year old. More precisely, the studies reported that male and female dogs spayed and neutered before 1 year of age had a higher incidence (1 in 4 chance ) of developing osteosarcoma! This suggests that sex hormones play a role in the the inhibition of bone cancer. Studies are currently underway to investigate the genetic susceptibility to osteosarcoma in Rottweilers and other breeds by fundings organized by the Canine Health Foundation and the Morris Animal Foundation.
Owning two rotties, respectively spayed and neutered before 1 year of age, seems to make statistics quite scary for their future. So I have learned my hard lesson, and now I am always worried sick that one day or another one of my Rotts will start limping and showing signs of this devastating condition.
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This article is accurate and true to the best of the author’s knowledge. It is not meant to substitute for diagnosis, prognosis, treatment, prescription, or formal and individualized advice from a veterinary medical professional. Animals exhibiting signs and symptoms of distress should be seen by a veterinarian immediately.
Questions & Answers
What's your opinion on amputation in osteosarcoma cases? It seems to delay the inevitable a few months.
Amputation removes the main source of pain so it offers quality of life. And dogs on three legs tend to do great, especially if it's the front leg to be amputated. Left untreated, the bone with the osteosarcoma will likely fracture (pathological fracture). Not all dogs are good candidates for the surgery, so this is something to discuss with a veterinary surgeon/veterinary oncologist.Helpful 2