The most prevalent form of bone cancer, osteosarcoma, accounts for only 5% of all canine tumours but its ability to spread quickly through the dog’s body makes it a silent and speedy killer.
If bone cancer was not so aggressive the amputation of an infected limb would be an adequate way to ensure a dog's survival. However, research shows that it is invariably the metastatic nature of bone cancer that kills and usually metastases of the lung.
For this reason, in most cases, amputation is followed up with some form of radiation or chemical therapy.
What causes bone cancer in dogs?
A definite cause of bone cancer has not been found. However, there are some factors suspected of encouraging a cancer to form, and some trends have also been noted. Here follows a list of the most documented:
- Spayed female dogs are more likely to contract bone cancer than male dogs
- Castrated male dogs show an elevated incidence
- Dogs that have suffered fractured bones may be more prone
- Dogs with a high rate of growth (i.e. giant breeds) are more prone
- Dogs over 80 pounds are up to 60 times more likely to suffer bone cancer
- Dogs that have undergone surgery or have some form of implant are more prone
- Family lines of cancer sufferers have been observed
Bone cancers tend to form around areas where new bone is being produced. That leads some veterinarian researchers to speculate that during the regrowth of bone a genetic malfunction sometimes causes a cancer to develop.
Are certain breeds of dog more prone to bone cancer?
Without a cause we can only speculate about the type of conditions required of cancer growth, and study the trends of bone cancer in certain breeds:
- Saint Bernard
- Great Dane
- Irish Setter
- Great Pyrenees
- Bernese Mountain Dog
- Dobermann Pinscher
- German Shepherd
- Golden Retriever
What are the symptoms of bone cancer in dogs?
The symptoms of early-stage bone cancer are hard to detect. One of the earliest signs of a potential problem is a dog’s lameness. This can be accompanied by a painful swelling or mass at the site of the tumour but it is not always.
As the disease worsens lameness is observed to be, ‘progressive, relentless and responds poorly to conventional pain killing drugs.’
Bone cancer of some parts of the skull of a dog is more easily detected because it impedes the animal’s ability to chew and swallow. Cranial cancers also affect a dog's behaviour.
Similarly, cancers of the pelvic area cause a dog pain when she urinates or defecates.
As the cancer worsens, and around three months after the tumour’s development, a dog exhibits signs of intense pain, and her lameness is constant. The risk of cancerous infection of other organs increases steadily.
What tests are carried out to confirm bone cancer?
If bone cancer is suspected, a round of tests needs to be performed to confirm the initial suspicion. Bone cancer may not be the cause of your dogs lameness: the symptoms of fungal bone infections are similar to those of cancer and such an infection looks similar to cancer from X-ray results. Your vet will probably carry out the following procedures to determine:
- Whether bone cancer is the cause of your dog’s symptoms or whether something else is at play
- What parts of her body the cancer has affected
- At what stage the cancer is, which includes:
- X-rays (of bone and of lungs to determine metastatic prevalence)
- Examination of bone biopsy (to identify the type of tumour)
- Blood tests
- Bone scan
Unfortunately by the time a dog is diagnosed with bone cancer the vet must assume that the cancer has spread to other parts of her body, in particular her lungs.
Research shows that up to 90% of dogs will have tumorous metastases of the lungs by the time of their diagnosis. Secondary lung cancer is the primary cause of canine death.
Following a positive diagnosis of cancer, surgery to remove the affected limb is the most commonly chosen route. However, simply removing the limb does not cure the canine patient because the cancer has probably spread to other areas. Therefore, a course of radiation or chemotherapy is administered to combat the metastases.
Some vets may choose not to remove the limb for various reasons. It could be that the tumour has been caught in its early stage and has not spread, or the tumour is confirmed to a small and distinct portion of bone.
In cases such as these an operation to remove part of the infected bone is performed. The section is replaced with a metal implant, which is often accompanied by a small sponge-like device diffused with a chemotherapeutic drug.
Some research suggests that dogs that have undergone surgery and chemotherapy live the longest (up to one year after surgery). On average, three quarters of the dogs that have surgery live for an average 138 days. The prognosis for dogs with bone cancer is determined by factors such as the dog’s age and how far the disease has progressed.
If you are concerned about your dog’s health and suspect bone cancer is the cause of her behavioural changes and lameness you should waste no time in seeking veterinarian help.
Your vet will advise you of the dog’s chances of recovery after determining the stage of her cancer, and they will recommend to you the most up to date remedies.