Canine Osteosarcoma (Bone Cancer)
Osteosarcoma is the most common primary bone tumor in dogs. Large and giant dog breeds have the highest risk of this malignancy. This tumor is locally destructive to normal body tissues and has a high metastatic rate (tendency to travel to distant sites in the body). It is one of the cancers in dogs that can be painful when in its active stages. Bones in the limbs that are affected by osteosarcoma can be weakened to the point of fracturing (called a pathological fracture). Osteosarcoma is an aggressive cancer that can develop in any bone of the body but the majority is seen in the limbs (e.g. elbow or the knee) where it is referred to as “appendicular osteosarcoma”. This is a very aggressive tumor that can cause lysis (disintegration of bone) and /or bone production, and it becomes more painful as it progresses. The lameness goes from intermittent to constant over 1 to 3 months. Obvious swelling becomes evident as the tumor grows and normal bone is replaced by the cancerous growth.
If no treatment is rendered, the animal usually succumbs to the disease within 1-2 months from the time of diagnosis. Surgical resection of the tumor and/or limb amputation are key to the treatment of osteosarcoma. Though many owners are at first hesitant about surgery, they frequently observe that their dogs improve dramatically after this treatment. This is by and large because a source of constant pain has been removed. Patients generally make a dramatic recovery within 10-14 days of surgery. It is important to note, however, that surgical resection alone does little to prolong the dog’s survival time.
Diagnosis
The initial evaluation of possible osteosarcoma involves x-rays of the affected site. The X-rays often reveal a characteristic bone pattern that, combined with history and breed, may indicate the presence of an osteosarcoma. While the history, physical examination, and x-ray findings may all point to the diagnosis of osteosarcoma, the only way to confirm the diagnosis is by biopsy.
What evaluation is needed for a pet with bone cancer?
In order to prepare a treatment plan for the pet, it is important to evaluate whether the cancer has spread to other organs. Osteosarcomas are known to metastasize to the lungs so chest X-rays are typically done to check if such spread occurred. Recently, advanced imaging techniques such as CT and MRI are being used to assess lung metastases and to evaluate the pet’s condition in more detail. The malignant growth in the bone may also be due to cancer that spread from other parts of the body. Common sites for these metastases are the lumbar and sacral vertebrae, pelvis, and the shaft of long bones. Assessment of the overall health and any co-existing medical conditions is critical to determine the appropriate course of treatment.
What about chemotherapy?
Osteosarcoma is always considered to have spread microscopically in the dog’s body by the time the diagnosis is made. This is the reason that surgery alone fails to control the disease. To attack the cancer cells both locally and systemically, chemotherapeutic agents can be used. The goals of therapy are to preserve a good to excellent quality of life for the dog, eliminate pain, and provide as long of a remission time as possible. A cure is not a reasonable goal at this time, and this fact must be realized by the owner prior to initiating therapy. The two most common chemotherapy agents used for osteosarcoma are doxorubicin (Adriamycin©), and platinum compounds such as carboplatin. Doxorubicin and the platinum compounds act synergistically against this type of cancer and they are used together for this purpose.
A total of 3 to 6 treatment sessions are scheduled at approximately 3-week intervals. The first treatment ideally begins about the time the surgical site sutures are removed. Although this protocol mirrors that used in humans, it is usually extremely well-tolerated. The patient’s quality of life is generally good to excellent as well as pain-free.
Other Medications
After chemotherapy, using a daily anti-inflammatory drug such as piroxicam or meloxicam (Metacam®), along with a low dose of antibiotic doxycycline is recommended. Together, these agents have been shown to reduce the growth rate of metastatic tumors. Side effects are uncommon with this combination, but if you detect that your dog has a decreased appetite, an increase in vomiting, or has dark, tar-like stools then stop the medications and alert us.
Side Effects of Therapy?
Healing from surgery is usually rapid and complete. The results in terms of cosmetics, function, and owner acceptance are excellent in most cases. All chemotherapeutic agents have potential side effects, which should be understood by the owner so that proper intervention can occur if the need arises.
Other Therapy
Radiation therapy is reserved primarily for relieving bone pain at the site when removal is not possible or elected. It is well-tolerated, but not curative.
Post-Therapy
After therapy sessions are completed, your dog should be monitored by us or your local veterinarian about every three months. Chest radiographs (x-rays) are generally done at these times to detect possible disease metastasis. As importantly, doctors love to see how their K-9 and feline survivors are enjoying life.
What is Life Like for Chemotherapy Patients?
Chances are that you, or someone you know, have experienced chemotherapy for the treatment of cancer. Veterinarians who treat animals for cancer use many of the same chemotherapy agents that human oncologists use. Yet, in many ways, the experience for pets seems very different. Why? For one thing, dosages of chemotherapy agents used in animals tend to be much lower than those used in people. Humans are given the highest doses possible, the consequences of which may require bone marrow transplantation, extended hospitalization, and numerous costly medications-all with good cause. However, for veterinary patients, this process would be unacceptable and cost-prohibitive for most owners. The general quality of life for many veterinary cancer treatment patients can be surprisingly good and very close to normal. Most of the time they can maintain their normal activities, travel, and have fun with their families who love and care for them.
Most currently used anti-cancer agents do not specifically target cancer cells. Rather, they target and damage or kill rapidly growing cells. For the patient, this means cells lining the stomach and intestine (high turnover rate), cells of the bone marrow that make up the immune system (white blood cells, in particular), and cancer cells. It then is little surprise that the most common side effects of chemotherapy agents include mild to moderate nausea, vomiting, diarrhea, and increased risk of infection. Hair loss, in contrast to humans, is uncommon in dogs and cats on chemotherapy. In most animals, hair does not grow continually throughout their lives as it does in people. Some breeds, however, are susceptible to at least some hair loss (especially poodles, sheepdogs, Scotties, and schnauzers). If your pet requires a groomer to trim its hair coat – then some hair loss can be anticipated. Pets, however, are not bothered much by this – and they seem to enjoy stylish polar-tec jackets as gifts. The good news is that normal cell lines can almost always regenerate themselves, while the less well-organized malignant cells suffer great damage. However, even at higher dosages, microscopic malignant cell clones remain alive, albeit dormant in the body. Eventually, these give rise to drug-resistant cell lines. This is the biological basis of recurrent or metastatic cancers.
Although there is a risk of side effects, the majority of patients complete their therapies without major complications. If they do occur, however, you should be prepared to recognize them and take appropriate action. Over time, the tendency is to have less frequent side effects, as the individual animal’s sensitivity to the drug agents becomes known, the treatments are less frequent, and the cancer is in remission.
Risks to People Living with Chemotherapy-Treated Pets
The anti-cancer drugs are excreted from the animal’s body via urine and feces. This usually happens in the 48 hours following treatment, but can be as long as 5 days for Adriamycin. If it is possible, you should try to have the animal eliminate in an area away from the immediate yard or play area. Cat boxes should be changed regularly, and waste material handled with a scoop. If urine or feces must be handled, use heavy rubber or latex gloves and disposable wipes/towels. Place all waste/towels in a plastic bag and seal it, before disposal. Smooth surfaces may be washed with a dilute bleach solution (1/4 c. to 1 gallon of water). Humans and other household pets living with treated pets are generally thought not to be at any health risk, just as in the case with humans. Pregnant women and children under the age of 18 should not handle ANY animal waste or anti-cancer medications. If any family member living with the pet has a condition that would suppress his/her immune system, it would be prudent to let the veterinarian know.
Prognosis
Unfortunately, virtually all animals diagnosed with osteosarcoma will eventually lose their battle with this disease. However, with appropriate intervention, most patients experience a high quality of life during their disease remission.
The median survival times (MST) are as follows (used as guidelines only):
| Treatment | MST (Days) | % alive at 1 year | % alive at 2 years |
| Surgery & Chemotherapy | 262-540 | 32-62 | 10-28 |
| Surgery Only | 101-175 | 11-21 | 0-4 |
| Radiation Therapy | 122-313 | – | – |
| Pain Control Only | 107 | – | – |
Is It Worth It?
This is a difficult question to answer. Every situation and client-pet relationship is different and must be dealt with individually. If it were ever obvious that therapy was not working, or that the pet was indeed experiencing pain or discomfort, we are ethically obligated to inform you. What we can say is that most pets do indeed appear to enjoy their extended life period and do not even realize that they are “ill.” However, the owner(s) must believe that they are doing the right thing for their pet and for their situation.
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Colorado State University’s Flint Animal Cancer Center has created a series of videos that answer common questions about limb amputation. The videos illustrate expectations two weeks before, during, and after limb amputation. To view the videos, please click on the link below: