Bone cancer is a common cancer in dogs, especially in large and giant breeds. Approximately 85 percent of canine bone tumors are osteosarcomas (osteo = bone, sarcoma = cancer). Osteosarcomas are highly aggressive tumors, characterized by painful bone destruction where the tumor grows. Osteosarcoma commonly affects the limbs of dogs but can also occur in other parts of the body (skull, ribs, vertebrae, pelvis). It happens in smaller dogs but much less commonly than in larger breed dogs.  In about 80 percent of patients, the cancer will spread to the lungs. The biological behavior, prognosis, and treatment of bone tumors depend on tumor type, primary location, and extent of disease spread. Various diagnostic tests such as X-rays, blood tests, and sometimes a biopsy are required to determine the most appropriate treatment.

Clinical Signs

The signs associated with a bone tumor may be nonspecific. A swelling, soft or hard that increases over time, can be associated with a bone tumor wherever it grows on the body.  These tumors are usually painful because the cancer is destroying the healthy bone. Limb tumors usually cause various degrees of lameness that may be intermittent initially, and it may improve in the short term with pain medications prescribed by your veterinarian. As the degree of discomfort increases, it can cause other signs such as irritability, aggression, loss of appetite, weight loss, sleeplessness, or reluctance to exercise.  Some dogs may present to the veterinarian due to a fracture caused by the weakening of the affected bone. Other clinical signs may vary, depending on the primary site and involvement of underlying structures.

Diagnosis and Staging

Initial evaluation of a dog with a suspected bone tumor often includes a complete physical examination, blood tests, X-rays (of both the affected site and the lungs), a bone scan to look for other areas of bone involvement, and sometimes a fine needle aspirate or biopsy.  A PET-CT scan may be offered to evaluate the entire body for the presence of spread. Definitive surgery, such as amputation in the case of a limb tumor, may be performed without a prior biopsy if the age, breed, location, and appearance of the tumor are all very suggestive of osteosarcoma. Work-up and staging are essential for two reasons. First, it is necessary to determine the tumor type and extent of the cancer. Diagnostic testing also provides the oncologist with information regarding the dog’s general health and may identify concurrent medical, bone/joint, or nerve/spinal problems, all of which may influence the treatment recommendations.

Treatment of Primary Canine Bone Tumors

The goal of treatment for every patient at the Flint Animal Cancer Center is to help every pet live the longest and best quality life possible despite both the cancer and the treatment.  In the case of bone tumors, there are many options, and our team of experts will explain all of them to you, including the pros and cons for your pet and family, and help you make an informed decision.  Pain management is always part of the care plan, and our team is here to help and support owners every step of the way, including end of life decisions. It’s our commitment to compassionate care.

Limb osteosarcoma commonly causes lameness and pain because of the invasion and destruction of healthy bone, necessitating a local treatment for the primary tumor. It is also a highly aggressive form of cancer that has a high metastatic rate requiring systemic therapy (chemotherapy and/or immunotherapy) to help slow the spread of the bone tumor cells in addition to the local treatment of the primary tumor.  Local treatment of the primary tumor alone has a median survival time of about four months, while the addition of chemotherapy can extend survival time to a year or longer.

The best option is case and patient-specific and typically involves surgery (such as a limb amputation) or radiation therapy. In the case of limb tumors, surgical or radiation limb-sparing options may be possible.   In our experience, many owners have a harder time with amputation for a limb bone tumor than their pets!  Most patients tolerate an amputation and even thrive once the painful tumor and limb are removed.  This, however, is not universally true, and a discussion with your oncologist and also a consult with a veterinary physical therapist and/or orthopedic specialist can contribute to the conversation about what is best for any individual patient. In most situations, dogs with three legs can do virtually everything that 4-legged dogs can do.

Dogs with tumors of the distal radius (lower forelimb) may be candidates for a limb-sparing surgical or radiation procedure. The surgery serves two purposes; it removes the primary tumor, which is necessary for cancer control, but it also eliminates the source of pain, and may, therefore, dramatically improve the quality of life. However, this option is dependent on the specific location and also requires intense follow-up care to help decrease the rate of complications.

Sometimes 3-5 high doses of a well-tolerated form of radiation therapy can be used to “kill” the tumor in the bone and also alleviate the pain.  This, however, requires that enough good bone exists to support the weight of the animal after treatment as the risk of a fracture remains.  Palliative radiation therapy is intended primarily as a pain management treatment. It has a significant benefit in approximately 75 percent of dogs for an average of 2-4 months, at which time it may be repeated. This therapy, when combined with an injectable drug called zoledronate, decreases bone destruction and has been shown to improve cancer-related bone pain in humans.

Chemotherapy is commonly used as an adjunct to a primary therapy like surgery or radiation therapy to slow the rate of metastasis for any bone tumor, which, unfortunately, is common with bone tumors.  Chemotherapy is unlikely to cure most dogs with osteosarcoma but can prolong a good quality of life. The most commonly used drug is an injectable medication called carboplatin, which is given once every three weeks for a total of four treatments. Most dogs tolerate chemotherapy well, with some dogs experiencing mild, self-limiting side effects such as depressed appetite, nausea, occasional vomiting, and diarrhea for a few days. Less than five percent of dogs will experience severe side effects requiring hospitalization. If severe side effects occur, the dosages of these drugs can be reduced in the subsequent treatments.

Following the completion of chemotherapy, we recommend regular monitoring for evidence of recurrence or metastasis.  Your oncologist will set a recheck schedule that is right for your pet, given their specific medical needs. The average survival time in dogs with osteosarcoma treated with surgery and chemotherapy is approximately one year. However, 20-25 percent of dogs may live longer than two years.

Canine Cancer Clinical Trials

Clinical trials offer another treatment option. Clinical trials are research studies that provide patients access to new and promising treatments for cancer. It is an opportunity for a potentially better outcome and helps to contribute to science to benefit future cancer patients. The Flint Animal Cancer Center offers 20-30 clinical trials for a variety of tumor types at any given time. Learn more about current clinical trials at the Flint Animal Cancer Center.

The CSU Flint Animal Cancer Center

The Flint Animal Cancer Center’s comprehensive clinical practice offers specialists in medical, surgical, and radiation oncology that work together as a unified team to develop a personalized diagnostic and treatment for every patient. The center offers the latest treatments in chemotherapy, surgery, and radiation for both common and rare cancers. If you are concerned about your pet’s health, the best first step is to schedule an appointment with your local veterinarian.