osteosarcoma

How do we Treat the Pain?

Keep in mind that dogs are usually euthanized due to the pain in the affected bone. Treating the pain successfully will allow a dog to live comfortably and extend life expectancy by virtue of extending comfort. There are two ways to address the pain: amputatating the limb and palliative radiotherapy (usually combined with periodic bisphosphonate infusion treatments).

For most patients, there is one tumor on a leg and no visible tumor spread in the lungs. These are the patients with the best potential results and they are good candidates for amputation. Patients with a lot of arthritis in the other legs or with tumor spread evident in the chest already are probably not candidates for amputation and it may be more appropriate to keep the leg and simply relieve the pain with radiotherapy.

Amputation of the Limb

Since the tumor in the limb is the source of pain, it makes sense that amputating the limb would resolve the pain. In fact, this is true. Removing the affected limb resolves the pain in 100 percent of cases. Unfortunately, many people are reluctant to have this procedure performed because of misconceptions.

• While losing a leg is handicapping to a human, losing one leg out of four does not restrict a dog's activity level. Running and playing are not inhibited by amputation once the surgical recovery period is over.
• While losing a limb is disfiguring to a human and has social ramifications, dogs are not self-conscious about their image. The dog will not feel disfigured by the surgery; it is the owner that will need to adjust to the dog’s new appearance.
• Median survival time for dogs who do not receive chemotherapy for osteosarcoma is 3 to 5 months from the time of diagnosis regardless of whether or not they have amputation. Do you want your dog's last 3 to 5 months to be painful or comfortable?

Read a letter about amputation from a veterinarian who sees too many owners who reject the option of amputation out of hand. His letter includes videos of two happy dogs without limbs.

Limb-sparing Surgery (Removing the tumor but not the leg)

Limb-sparing techniques developed for humans have been adapted for dogs. To spare the limb and thus avoid amputation, the tumorous bone is removed and either replaced by a bone graft from a bone bank or the remaining bone can be re-grown via a new technique called bone transport osteogenesis. The joint nearest the tumor is fused (i.e., fixed in one position and cannot be flexed or extended.)

• Limb sparing cannot be done if more than 50% of the bone is involved by tumor or if neighboring muscle is involved.
• Limb sparing does not work well for hind legs or tumors of the humerus (arm bone.)
• Limb sparing works best for tumors of the distal radius (forearm bone).
• Complications of limb sparing can include: Bone infection, implant failure, tumor recurrence, and fracture.

While amputation can be viewed as a pain management strategy, limb-sparing is only performed in conjunction with chemotherapy. It is important to keep in mind that grafting of a new bone structure requires healing time and that a great deal of post-operative confinement time is needed (in a patient whose life expectancy is going to be measured in months). For the right patient, limb-sparing can be the best choice but be sure to understand all the details of post-operative care from the specialist.

Palliative Radiotherapy for Pain Control

Sometimes amputation is simply not the right choice and happily there is an effective alternative treatment. Radiation can be applied to the tumor in two, three or four doses, depending on the protocol. Improved limb function is usually evident within the first 3 weeks and typically lasts 2 to 4 months. When pain returns, radiation can be given again for further pain relief if deemed appropriate based on the stage of the cancer at that time. There are a couple of caveats:

• When pain is relieved in the tumorous limb, there is an increase in activity that can in turn lead to a pathologic fracture of the bone.
• Radiotherapy does not produce a helpful response in about 1/4 of patients. Remember, amputation controls pain in 100 percent of cases but if amputation is simply not an option, there is a 3 out of 4 chance that radiotherapy will control the pain.
• Current standard treatment involves pairing palliative radiation with monthly infusions of medications called bisphosphonates.

Bisphosphonates

This class of drug has become the standard of care in humans with bone tumors and have been found helpful in managing osteosarcoma pain in dogs as well. Bisphosphonates act by inhibiting bone destruction, which in turn helps control the pain and bone damage caused by the bone tumor. The most common bisphosphonate in use for dogs has been pamidronate, though a new drug zoledronate is taking its place gradually. Treatment is given as an IV drip over two hours in the hospital every 3 to 4 weeks. In humans, an assortment of potential side effects have emerged (fever, muscle pain, nausea all lasting 1 to 2 days in up to 25 percent of patients, renal disease in certain situations, low blood calcium levels, jaw bone cell death); these issues so far have not panned out as problems for dogs and cats. Bisphosphonates are important in managing bone tumor pain in patients that have no undergone amputation.

Analgesic Drugs

At this time there are numerous analgesic medications available for dogs with this tumor. No single medication, however, is a match for the pain involved in what amounts to a slowly exploding bone. A combination of medications is needed to be reasonably palliative and should be considered only as a last resort if amputation or radiation therapy will not be pursued. There are several types of drugs that can be combined.

• Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) These are anti-inflammatory pain relievers developed for dogs: carprofen, etodolac, deracoxib, meloxicam, firocoxib, and others. These are typically given once or twice daily in tablet form at home. The patient should have good liver and kidney function in order to take medications of this class.
• Narcotic Pain Relievers While these drugs do not have anti-inflammatory properties, they are well-known analgesics and have been used in an assortment of forms for thousands of years. They are particularly useful in chronic pain because they do not interact negatively with other pain relievers. Drowsiness is a potential side effect. Tramadol has been particularly popular as part of a drug combination for bone cancer pain but there are other narcotics that might also be considered.
• Miscellaneous Supplemental Pain Relievers There are two drugs that have surfaced as adjunct pain relievers for animals with chronic pain: gabapentin and amantadine. Gabapentin works on neurologic pain and is rapidly surfacing in the treatment of arthritis, surgical pain, and other chronic pain states. Amantadine works by reducing what is called "wind up," a phenomenon where nerves become sensitized to pain leading to the experience of pain from stimuli that normally do not cause pain.

These different drugs are often given together to create analgesia to the osteosarcoma patient when amputation and radiotherapy are not going to happen. It is important to realize that there is a limit to how much pain relief can be achieved against a bone tumor with only pills. It will not be long before the pain of this tumor, as evidenced by not using the leg, tenderness to the touch, etc., overpowers the effect of oral medications.

Treating osteosarcoma is an area that not all veterinarians are comfortable performing. Discuss with your veterinarian whether referral to a specialist would be best for you and your pet.