Osteosarcoma is one of the most common canine cancers encountered by veterinary oncologists. It's most common in the "long bones" or legs of dogs but can show up in any bone, including the jaws, hips, or pelvis. Advanced cases can move beyond bone lesions and can affect the lungs, spleen, liver, kidneys, and other organs.
For a dog, osteosarcoma is typically quite painful. Many dog owners notice a problem because their dog starts favoring a limb, exhibiting lameness, or has distinct swelling in a limb. They're also frequently lethargic and hesitant to do any activity that involves the affected limb.
Unfortunately, the cancer is extremely aggressive. By the time it's noticed and diagnosed, it has almost always spread, though often invisibly. The prognosis is often not great.
Traditionally, the most common treatment for limb-based osteosarcoma is amputation of the limb. While this is often unsettling for pet owners, dogs adapt quickly and commonly do well after the removal.
Saving a Limb with Osteosarcoma
There are, however, options for removing a tumor in a leg without removing the leg as a whole. These are called "limb-sparing" or "limb salvage" surgeries. There are several different kinds of limb-sparing procedures, with different pros and cons.
Limb-sparing surgeries are generally used in cases where a tumor is caught early, the prognosis is more positive, and they meet other qualifications.
"The goal of limb-sparing is to reduce pain or completely remove the diseased bone and surrounding tissues while still preserving the function of the remaining limb. The piece of diseased bone that is removed is replaced by a combination of healthy bone from a donor and bone graft from other parts of the patient's body. While much of the leg's function is preserved, there is a decreased range of motion in the treated limb. This can result in limited activity for the dog." - OncaLink.
As with any significant surgery, there are always risks of side effects. Those side effects also vary depending on the method used for limb-sparing tumor removal.
How can a dog be qualified for limb-sparing surgery?
Since osteosarcoma is so aggressive, not all dogs qualify for limb-sparing surgery. They must meet numerous qualifications, including:
A tumor that is not too large, does not affect too much bone, and is positioned on a long limb bone in a place where it can be removed without excess hazard to the dog.
Consensus between primary care vet, surgeon, oncologist, and pet owner that the treatment is the right way to go. If there's disagreement, the surgery is unlikely to be approved.
Imaging and planning, often including CT and MRI, to verify that the tumor is isolated, removable, and hasn't spread.
Positive bloodwork. Since serious surgeries like this require anesthesia, the dog in question must be healthy enough to survive being put under and recover afterward.
If a dog qualifies and is approved, a decision must be made regarding which procedure to use.
Evaluating a dog with osteosarcoma requires a comprehensive approach. Initially, a physical examination is conducted to assess the dog's general health. This is followed by a series of tests, including a complete blood count, serum biochemistry profile, and urinalysis. While these tests are crucial for understanding the overall health status of the dog, it's important to note that they do not directly determine if the cancer has metastasized (spread to other locations). They are, however, essential steps in the preliminary assessment before devising a treatment plan.
For a more detailed assessment of the cancer's stage, including its spread, imaging techniques are employed. These include thoracic radiographs (chest X-rays), abdominal ultrasound, or a full-body CT scan. These imaging methods are effective in detecting larger secondary tumors, although they might not reveal microscopic metastases. Understanding the extent and spread of osteosarcoma is vital for selecting the most appropriate limb-sparing treatment strategy.
Currently, there are four variations of limb-sparing surgeries. Let's evaluate their mechanics, pros, and cons.
Option 1: Cadaver Bone Replacement
The first option is a kind of bone replacement surgery. This surgery is similar to an organ transplant, except with a section of bone. The affected bone and tumor are cut away, and an equivalent section of bone from a deceased dog of the same breed and compatible genetics will be inserted in its place. Over time, the transplanted bone will heal and join to the original bone, restoring the limb to functionality.
This method has been commonly used and is one of the oldest limb-sparing techniques. However, it has largely been supplanted by more modern techniques due to the problems and complications it can cause.
The biggest benefit to this method is the use of organic material, which can heal and function relatively like normal.
The downsides are, unfortunately, severe.
There must be an available donor bone, which is not always easy to come by, particularly for larger or rarer breeds.
There is an extremely high – 50% or more – risk of infection. Moreover, the infection is likely to be chronic and untreatable.
Due to this infection risk, this is not a good technique; other options should be considered instead.
Option 2: Patient Bone Replacement
Similar to the first option, another way to replace a removed segment of bone can be considered. In this case, however, donor bone is taken from the patient's other bones. For example, if the tumor is in the radius, donor bone may be taken from the adjacent ulna.
This method is an improvement over a cadaver donor for two reasons. First, the donor bone comes from the patient, so the risk of rejection and infection is minimal in comparison. Second, with careful surgery or microsurgery, the blood supply to the donor bone segment can be either maintained or restored, keeping the bone alive and healthy. Healing is faster, and the bone will become more weight-bearing than other strategies.
The biggest downside to this method is the intensity of the procedure. First, the surgery must be well-planned to ensure that it can even be done. If it can, it needs to be done very carefully; the surgeon generally must be capable of microsurgery, and the process is long and intense.
When done properly, complications are minimal, healing is fast, and the limb is strong. However, the qualifications required to be able to perform this surgery are high.
Option 3: The Ilizarov Technique
A technique used in human medicine and now in canine medicine is the Ilizarov technique. It is so named because it relies on circular, external bone fixators that were invented by Gavril Ilizarov in the 1950s.
This technique is a combination of internal growth and external fixation. First, the tumor and affected bone are removed. Then, another cut is made, and the bone is gradually separated. Natural healing attempts to knit the bone back together, but the "target" is moved to extend bone growth to fill the gap. Along the way, external fixators are screwed into the bone and to metal supports, which provide the actual support of the limb while the healing happens.
"The Ilizarov method is a surgery involving an orthopedic external fixator applied to the limb to reconstruct, reshape, or lengthen bones (usually of the limb).
External fixation is a surgical treatment where rods are screwed through an incision into the affected bone and exit the body to be attached to a stabilizing structure outside of the body.
Ilizarov surgery involves the use of a special device called an 'Ilizarov apparatus or Ilizarov fixator.' It is recommended in cases that are not amenable to other reconstruction techniques." – Golden State Ortho.
When all is said and done, the bone will have grown to replace the bone removed, and the limb will be whole again. The external fixators can be removed, the wound will heal, and the limb will be restored.
When done properly, this method can be very effective. Because it's a natural healing process, the resulting bone can be strong and functional.
The biggest downside to this option is how long it takes. Fixators penetrate the skin and present an infection risk until they are removed, and the adjustment during the process can be rough. The process can take 4-6 months, with additional healing after the fact. In many cases, this can be longer than the prognosis for advanced osteosarcoma cases, which is why this procedure is not always recommended.
Option 4: Metal Implants
The fourth and final option is a metal implant. Human medicine has used these for quite some time, including hip replacements and other common surgeries. For a dog with osteosarcoma, the affected bone can be removed, and a construct of plates and rods can be inserted in its place.
This option is the newest being developed currently. It is showing promising results, but as of yet, no commercially available implants have been approved. It's the procedure to keep an eye on.
Are There Other Procedures Being Developed?
Of course. Medical science is progressing on all fronts, and many novel treatments are being explored.
One such treatment is known as Histotripsy. Histotripsy uses powerful ultrasonic applications to physically break down the tissue of a solid tumor in the bone. The body then seems to induce an immune response that destroys the cancerous cells and can potentially cascade to destroying the same cells systemically, similar to how a vaccine works.
This method is being explored and is not currently fully approved for use. It is currently approved for use on liver cancers in humans but not for any other use or for canine use.
"Histotripsy offers a promising alternative to cancer treatments such as surgery, radiation and chemotherapy, which often have significant side effects. FDA officials on Oct. 9 awarded clearance to HistoSonics, a company co-founded in 2009 by U-M engineers and doctors for the use of histotripsy to destroy targeted liver tissue." – University of Michigan.
That said, clinical trials are ongoing to determine if it might be viable for treating various kinds of cancers other than liver across species.
"Even though bone tumors in general and those that were studied vary in their make-up with different amounts of normal structure, softened bone, and cancerous cells, histotripsy treatment resulted in complete disintegration of the targeted tissue. There was no evidence of damage to the overlying muscle or skin layers. Even samples of normal muscle and nerve tissue showed no evidence of damage after treatment with the histotripsy parameters used to target bone cancer, demonstrating that the treatment can be very tissue specific." – American Kennel Club Canine Health Foundation.
Another option is immunotherapy. Immunotherapy develops a customized vaccine for a cancer diagnosed in a patient and trains that patient's immune system to identify and attack that cancer as an abnormal kind of cell. This is doubly beneficial because the immune system is much more thorough than any human treatment like surgery or radiation can be; it can even catch cells individually before they develop into larger tumors.
Progress is slowly being made on a variety of immunotherapy options, including options for osteosarcoma. For example, ELIAS Animal Health is producing the ECI Treatment, which is a personalized, bivalent treatment for cancers such as osteosarcoma.
With a wide range of new treatment options on the horizon, prognoses for canine osteosarcoma are looking better than ever with each passing year. While we're still a long way off from having "cured" any kind of cancer in dogs or in humans, the next few years are likely going to see even more unique and novel developments in the field of canine cancer treatments.
Navigating Upcoming Developments
As a vet, you want to do what's best for your patients. However, unless you're an oncologist, chances are good that you aren't keeping up to date on every new potential treatment option.
Therefore, there are a few options available to you.
You can start watching the news. While this can help keep you abreast of upcoming options, it can take away from other areas of expertise for your practice.
You can partner with a veterinary oncologist who keeps up with new treatments and clinical trials. By partnering with an experienced and effective canine oncologist, you can refer patients as they are diagnosed and trust that they're in good hands.
You can work with us.
At Hope Vet, we provide consulting, second opinions, and additional diagnoses for dogs with all kinds of cancer. Our oncology specialists can also help by recommending potential treatment options, including novel treatments, nearby clinical trials, and other possibilities.
In addition to canine oncology, our team can also help you with dermatology, neurology, internal medicine, and a variety of other areas of expertise. If you're interested in a consultation, simply click to request one in the menu above. We look forward to hearing from you.