Thus far I’ve discussed various methods we use to diagnose dogs with osteosarcoma and the staging tests required to look for spread of this disease. In the following two articles I will describe palliative and definitive treatment options for this disease, and their respective prognoses.
To review, osteosarcoma is an aggressive form of bone cancer in dogs. Most tumors arise within weight-bearing bones, and the majority of dogs are presented to their veterinarians because of lameness. In most cases, the recommendation will be to amputate the affected limb, and with this surgery, the expected prognosis is about 4-5 months.
The short survival time is because this cancer usually has already spread to distant sites in the body before we are able to detect it. Amputating a limb without further therapy is considered palliative treatment, but remains the most effective way to remove the source of pain for the patient.
Many owners fear amputation, as they believe their dog will be unable to ambulate on three limbs, or that the loss of a limb will somehow alter their dog’s personality/demeanor. In my experience, this is exceedingly rare.
A very good resource of information about amputation is Tripawds, where the motto is “It’s better to hop on three legs than limp on four.” Here, owners of three-legged pets provide a fantastic support network for each other and for owners considering surgery. One can find a group of “peers” to bounce questions off of and read personal experiences on individual blog pages and forums. I also direct owners to search “Three-legged dogs” on youtube, as there are thousands of videos of dogs racing around after amputation, helping to support the notion that amputation is neither cruel nor debilitating.
For cases where amputation is not an option, or when owners will not consider this procedure, alternative palliative measures can be attempted as a means to reduce pain.
In human cancer terms, palliative treatments are designed to alleviate clinical signs related to the tumor(s), but are not necessarily expected to extend that patient's lifespan.
In veterinary medicine, if palliative options are successful in controlling pain related to cancer, patients will often live longer than they would if their signs were not controlled, simply because their quality of life is vastly improved and euthanasia can be delayed. Survival may only be extended by a few weeks to months, but for many owners this is exactly what they need to come to terms with the diagnosis and enjoy good quality time with their pets.
One very effective form of palliative treatment for dogs with osteosarcoma is radiation therapy. During radiation therapy, high-energy beams of radiation are applied to a tumor from an external source. Most facilities treating dogs with radiation use a linear accelerator machine. Treatment protocols vary, but may consist of one treatment a week for 4-6 weeks, or consecutive daily treatments for 2-5 days. Studies indicate around 70-90 percent of dogs will show improvement in their pain scores, with most dogs showing improvement with just one treatment.
Dogs can develop fairly significant localized skin reactions with this form of radiation, with hair loss, ulceration, scabbing, and swelling seen in many cases. Palliative radiation therapy also causes increased susceptibility to fracturing an already weakened bone. This is likely from a combination of activity and stress on the limb because the pet feels better, and because the radiation therapy could inherently cause damage to the bone.
Stereotactic radiation therapy is a newer form of radiation available at some university and referral hospitals. This form of radiation is more localized for treating the tumor while sparing the normal tissue surrounding the tumor, therefore less likely to cause some of the side effects listed above.
Bisphosphonates are intravenous or oral medications used to treat bone pain in dogs. Drugs in this class were developed to prevent osteoporosis in post-menopausal women. They work to inhibit bone resorption, which is one of the main sources of pain in bone cancer. These medications are extremely well tolerated, with minimal to no side effects, and when used as a sole treatment options, are successful in relieving pain in 40 percent of patients.
Oral medications are the mainstay of palliative treatment for dogs with osteosarcoma. Often we are prescribing a combination of pain medications that include non-steroidal anti-inflammatories, along with strong opioid or opioid-like drugs and neuropathic pain inhibitors. Long-acting analgesic nerve blocks can also be used.
Some veterinarians advocate the use of acupuncture, homeopathic remedies, and/or physical therapy for treating bone pain. I do not have personal experience with these options, but am always open to discussing pros and cons with owners.
I recommend a combination of all of the above-mentioned options for dogs with osteosarcoma, as I truly believe a multi-modality approach is most successful. Statistics will argue that dogs treated palliatively do not live longer than dogs that undergo surgical amputation alone (about 4-5 months). However, in my clinical experience the 4-5 months for dogs with adequate pain control are far more enjoyable than for those whose pain we cannot control.
Focusing back on our patient Duffy, I discussed palliative options with his owners, especially in light of the concern for the small lesion seen within one of his lung lobes.
As with most owners, their main concern was making sure Duffy remained pain-free for as long as possible. Although they weren’t quite sure they were ready to commit to chemotherapy after surgery, they were willing to take the risk in the face of possible metastatic disease and elected to move forward with amputation of his affected limb. We were able to perform surgery the very next day, making the time from when I met Duffy to his recovery from amputation (and beginning of time pain-free) less than three days.
Next week, in the final article in this series, I will discuss the chemotherapy options for treating dogs with osteosarcoma, and what Duffy’s owners ultimately elected for his long-term treatment plan.
Dr. Joanne Intile