Osteosarcoma, which is the most common tumor type, is highly malignant
Amputation for a highly malignant cancer such as osteosarcoma is the treatment of choice for most cases, but is largely palliative
Chemotherapy is needed to extend life of the patient in many cases
One study that evaluated owner satisfaction showed that nearly all owners were very pleased with their pet’s quality of life following limb amputation
Introduction
Bone cancer is common in dogs. Like humans, many types of bone cancer exist in dogs and cats. In fact, 10,000 new cases of bone cancer are diagnosed in dogs each year
There are two basic groups: primary, which originate from the bone and metastatic which originate from a cancer located in another part of the body, but have migrated to the bone.
Metastatic bone tumors may not be treated if extensive tumor involvement is present elsewhere in the body (see photo right – this is a case of multiple myeloma)
Primary bone tumors in dogs and cats usually comprise of osteosarcoma, chondrosarcoma, and fibrosarcoma. The different tumor types behave differently and the behavior may be dependant on the grade of tumor.
Osteosarcoma, which is the most common tumor type is highly malignant and about 95% of the dogs have metastatic disease (spread of this tumor) at the time of diagnosis. Most dogs that have Osteosarcoma will die from the metastasis of tumor to the lungs or other bones. Amputation of the limb will ameliorate the pain, but does not extend the life of the patient unless chemotherapy is also given. Osteosarcoma in the cat can potentially be cured with amputation of the limb alone, as the metastatic potential of the tumor in this species is much lower.
Chondrosarcomas generally have a less aggressive tendency to spread than osteosarcomas.
Fibrosarcomas generally are locally invasive and have a low tendency to spread unless the tumor is high grade.
Another type of tumor which causes bone destruction is the synovial cell carcinoma. Grade 1 and 2 synovial cell sarcomas have a good prognosis and are potentially curable, however grade 3 synovial cell sarcomas usually result in death of the patient within a couple of months. Right is an example of a hock joint that has been destroyed by a synovial cell sarcoma.
Signs of bone cancer
The first clinical sign of a bone tumor is usually lameness of the affected limb. Initially the lameness may be subtle, but then becomes progressively worse. Anti-inflammatory medication generally does not resolve the lameness. Some dogs develop acute nonweight-bearing lameness which is caused by bone fracture due to weakening of the bone structure by the tumor.
A swelling may also be noticed over the bone, but this is not always a consistent finding in the early stages.
As time passes on the dog may develop loss of appetite and significant weight-loss. These findings may be due to factors released by the tumor or due to pain caused by the tumor.
Bone cancer is very painful….just ask a human who has had it. Because this is a very painful tumor in dogs, surgery is usually recommended.
Diagnostic testing prior to surgery
Before bone cancer is treated a diagnostic work-up should be completed.
Chest x-rays are taken to ensure that there is no evidence of spread of cancer to the lungs.
X-rays of the affected limb are always taken. If your pet has been traveling in the southern United States there is a possibility that the abnormal appearance of the bone is not due to cancer, rather a fungal infection. In this situation the dog would be treated with medications. Note the large expansile tumor in the mid part of the radius bone (Fig 1), which is evidence of a bone tumor; in this case it was a neurofibrosarcoma, which is a less common tumor type affecting the bone.
Other diagnostics run include a complete blood cell count, chemistry profile to check the function of internal organs, and sometimes a urinalysis.
Ultrasound of the heart is done if Adriamycin is chosen as the chemotherapeutic agent, as this medication is contraindicated for dogs that have heart muscle disease called cardiomyopathy.
Nuclear scintigraphy or PET scan can be used to help rule out macroscopic spread of bone cancer.
If the appearance of the bone is not classic for a primary bone cancer, a biopsy to confirm this is generally done. Your pet would be anesthetized for this procedure and multiple small samples of the bone are collected and submitted for analysis by a pathologist. Bone biopsy is 90% accurate at arriving at a diagnosis, therefore 10% of the time the diagnosis of cancer will be missed when it really is present.
If the hind limb of your pet is going to be removed and your pet has had signs of stiffness of the hind limbs in the past due to hip problems, x-rays of the pelvis are generally taken to rule out other diseases. Arthritis that is not causing significant functional impairment of ambulation is not a contraindication to amputation.
Surgical treatment of bone cancer
Amputation for a highly malignant cancer such as osteosarcoma is the treatment of choice for most cases, but is largely palliative. That is, amputation is done to remove the pain that the pet is experiencing. In this situation it generally does not increase the length of survival of the patient. Chemotherapy is needed to extend life of the patient. Amputation for the less aggressive bone tumors should cure the patient of cancer. The dog in Fig 2 had an amputation one day prior to this photo and can already walk relatively well.
If your pet has bone cancer of the lower part of the radius bone, a limb sparing procedure can be done as an alternative to amputation. The cancerous portion of bone is removed and replaced with a living bone graft. Very good function of the limb is expected after the bone graft heals in place (2 to 3 months).
If you elect to not have the limb amputated and chemotherapy done, a couple of large doses of radiation can be administered to the site to decrease the pain. If no treatment is going to be administered to a pet that has bone cancer and the pet is in pain, euthanasia is recommended.
Palliative treatment of bone cancer
Palliative treatment is a means of making the pet more comfortable during the last phase of their life. This is utilized if the owners elect to not have surgery performed. In addition, if the patient already has spread of the cancer to other areas in the body, amputation of the limb may not be elected.
Palliative radiation therapy involves about 4 to 6 treatments (number of treatments may vary depending on the oncologists preference). This treatment will not eliminate the tumor rather, it reduces the pain in the bone by reducing tumor associated inflammation.
Bisphosphonates can reduce bone tumor-associated pain by strengthening the weakened bone. This medication inhibits the osteoclasts within the bone from dissolving the bone. Some dogs will have a dramatic improvement in clinical lameness with this treatment.
Analgesics such as narcotics (tramadol and codeine) and nonsteroidal anti-inflammatories (Rimadyl, Deramaxx, Piroxicam, Metacam, Previcox and others)
After care and convalescence
After surgery has been completed intensive care must be provided for the best chance for a successful outcome. Intravenous fluids may be continued over night to minimize dehydration.
Pain control after an amputation is very important in the postop period. Generally we place an epidural catheter or incisional catheter through which medication is administered to relieve pain. A pain patch can also be applied to the skin. The medication from the patch will slowly be absorbed into the body. Pain control from the patch will last about 3 days.
Medications at home:
If your pet has an incisional catheter or epidural catheter, medication will need to be administered by you for about 2 days via this port.
An oral nonsteroidal anti-inflammatory is prescribed for a period of 10 days to relieve inflammation related pain
Tramadol (narcotic) blocks pain perception at the level of the brain. Initially this medication is given four times daily for four days, then twice daily for one month.
Gabapentin is prescribed for one month after surgery. The gabapentin blocks amplification of pain at the level of the spinal cord
Occasionally a patient will experience phantom pain after amputation. For this reason, the tramadol and gabapentin are continued for one month after surgery
A bandage may be used to cover the incision for a day or two. The bandage should be kept clean, but should be changed if we feel that is needed.
Pets are usually hospitalized for 1 to 2 days following amputation and limb spare surgery
In general your pet will learn to walk with three limbs within a day or two. Older dogs may take a bit longer to learn to adapt to having three limbs. By 10 days after surgery these older pet also adjust to being able to walk well.
Chemotherapy
Chemotherapy is usually started 2 weeks after surgery by an oncologist.
In general chemotherapy is given every 2 to 3 weeks for a total of 5 or 6 treatments.
Adriamycin may be used as a sole agent, or alternating cycles of adriamycin and carboplatin may be used.
The oncologist may elect to choose a protocol that is different from the standard one if there is a need for this.
During chemotherapy blood work and potentially heart ultrasounds may be done to make sure that your pet is not having any side effects of the medication.
Side effects of the chemotherapy may include nausea, vomiting, loss of appetite, and infrequently heart problems if Adriamycin is used. Infections due to a low white blood cell count may also be a problem. Fortunately, side effects associated with chemo are not very common and if they occur are usually transient. Loss of hair (balding) generally is not seen in dogs. Breeds of dogs that have continually growing hair (example: poodle) may have transient thinning of the hair coat.
X-rays of the chest will be taken by the oncologist every 3 months to check for evidence of spread of cancer.
Potential complications
As with any surgery, complications may arise. Even though rare, anesthetic death can occur. With the use of modern anesthetic protocols and extensive monitoring devices (blood pressure, EKG, pulse oximetry, inspiratory and expiratory carbon dioxide levels, and respiration rate), the risk of problems with anesthesia is minimal.
Infection is also an unusual complication as strict sterile technique is used during the surgery and antibiotics are administered during the surgery.
Seroma formation can occur as there may be an empty space between the tissues. This problem will resolve with time. Occasionally the seroma or fluid that has build up may require draining. In cases in which seroma formation is expected a drain may be placed at the time of surgery.
Recurrence of cancer is not common at the surgery site, but this can also occur. More commonly the cancer spreads to another site such as the lungs or other bones. Signs of recurrence of cancer may include difficulty breathing, coughing, loss of appetite, weight-loss, and pain of the bones (which may present as lameness).
Owner satisfaction with amputation
One study that evaluated owner satisfaction showed that nearly all owners were very pleased with their pet’s quality of life following limb amputation.
Most dogs are able to run and play again.
Prognosis
Osteosarcoma
treatment with amputation alone – survival time of 3 to 5 months
amputation and chemotherapy – survival for about 1 year; occasionally we have seen dogs live 3 to 4 years following treatment
Chondrosarcoma and fibroscaroma
amputation can be potentially curative without chemotherapy
Synovial cell sarcoma
grade 1 and 2 tumors – frequently are cured with amputation alone
grade 3 tumors – regardless of treatment these patients usually die within a few months; median survival time has been reported to be 7 months
