Q: We live out in the country on a farm and have always had big dogs. Currently we have two Great Pyrenees that we love. We noticed a swelling and some lameness on the front leg of one of our dogs near her paw. We took her to the vet and they took some X-rays and said there was a good chance she had bone cancer. We are devastated. Can you tell us a little more about bone cancer and what our options are?
A: Tumors in bones of dogs can be either of primary origin, meaning they started in the bone and are growing and causing problems there; or secondary, meaning they started in another organ - like the liver, for example - and have spread to the bone in question.
There are several primary types of tumors and they include osteosarcomas and chondrosarcomas. Tumors that are secondary and spread to the bone include many carcinomas, such as squamous cell carcinoma. What is interesting is that primary tumors tend to be found at the ends of the bone on X-rays. Secondary tumors tend to be found in the middle of the bone on X-rays. This diagnostic feature tends to help the veterinarian only when making the diagnosis, unfortunately. All tumors in bones are critically aggressive.
The most common primary bone tumor is an osteosarcoma in the dog. Normally, osteosarcomas are found in large and giant breed dogs of middle age. They are not necessarily found in the older pets. They can be at the ends of any long bones, but the end of the forearm above the front paw and the top of the humerous or upper arm bone are two of the most common sites. Osteosarcomas will metastasize to the lungs as the disease progresses.
Clinically, theses dogs will present to the veterinarian for lameness and sometimes if it is later in the progression of the disease there will be some harder type of swelling associated with the area. Remember, these are usually big strong dogs that can be reluctant to show pain and some will continue to bear weight on the leg to some degree.
X-rays are so important to start the diagnostic process with these patients. Treating a bone tumor suspect with oral pain management alone will potentially delay treatment and lower survival time. If a bone lesion is visualized on an X-ray, the next step is a biopsy. A bone biopsy is the only way to get a definitive diagnosis of any tumor. Biopsies tell us the name of the tumor and therefore the suspected behavior and treatment options and prognosis.
After a definitive diagnosis is made, the first step to treating an osteosarcoma in the pet 99 percent of the time involves amputation of the limb. You must get rid of the tumor to stop pain and to stop or slow the spread of cancer. These pets are usually not walking on the leg anyway, so amputation is not as hard on them as it is on us.
After amputation, chemotherapy may be started both in the oral and IV form. Even with all theses efforts, this is a bad form of cancer. The goal of treatment is to decrease pain and increase quality of life for whatever time the pet has left. With amputation, aggressive chemotherapy and no evidence on X-rays that the cancer has spread to the lungs, survival times can be 10 to 12 months. If the limb is not amputated and there is spread to the lungs, the prognosis is poor, with survival times of fewer than six months.
I would encourage you to consider the lifestyle of your pet and the amount of discomfort he is in. Treat pain first and foremost, and if there is any hope that you have discovered this disease early, you may consider chemotherapy to help your pet.