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ABOUT THE PROBLEM
Bone cancer can be primary or secondary. Primary bone cancer arises within the bone, from any of the body tissues within or attached to bone. Secondary bone cancer is cancer that has started somewhere other than bone, and spread to bone.
More than 90% of cases of primary bone cancer in dogs are a particular type called osteosarcoma. Osteosarcoma is somewhat less common in other pet species, but is still the most common type of primary bone cancer in non-canine pets.
Bone cancer is almost always malignant. The most common site of metastasis in dogs is the lungs; bones other than the one that contains the primary tumor are the other common site for metastasis. By the time bone cancer is diagnosed it is extremely likely that it has already metastasized, even if diagnostic tests do not reveal this.
Regarding most primary bone tumors in dogs: more than 75% of them occur on a leg; the average age of appearance is 7 to 8 years, with a range of 6 months to very old; the breeds most commonly affected include Golden Retrievers, Labrador Retrievers, Great Danes, Rottweilers, Doberman Pinschers, German Shepherds, Saint Bernards, and Bernese Mountain Dogs; relatively tall individuals within a breed are more commonly affected.
We are often very certain of our diagnosis based on physical exam findings, but the exam is never a 100% certain diagnosis.
X-RAYS X-rays of the swollen region(s) of bone add significantly to the certainty of a diagnosis of bone cancer. While they might not technically bring this certainty to 100%, we believe for practical purposes x-rays are often definitive.
When we use x-rays to search for evidence of metastasis, we x-ray the chest, and the bones of the whole body. While metastasis to the chest is more common than metastasis to other bones, research indicates we can find evidence of metastasis in other bones earlier than we can find it in the lungs.
SURGICAL BIOPSY This is the only way to definitively diagnose a bone lesion as cancerous, and to determine what type of cancer it is. Biopsy is probably most important when treatment options other than palliative care are being considered.
Of special note, it can be surprisingly difficult to obtain a diagnostic biopsy from a bone tumor. The procedure for obtaining the sample is not usually particularly difficult, but sometimes a sample that appears to be more than adequate at the time of collection does not yield a diagnosis on the pathologist's exam. We have encountered cases that had to be biopsied two or three times before a diagnosis was obtained.
GENERAL LABORATORY TESTING A blood profile is a useful test for determining a patient’s over-all health status, and has particular value for helping us to determine the pet’s ability to tolerate the various treatment options that are being considered. Also, abnormally elevated levels of a couple of tests on a general profile are consistent with a worse prognosis for dogs with bone cancer.
ULTRASOUND EXAM Abdominal organs and other soft tissues are not common sites for metastasis of bone tumors in dogs. They are somewhat more common sites in cats and other pets. We believe it is worthwhile to also do an abdominal ultrasound exam as part of our screening testing for metastasis.
ADVANCED IMAGING CT scan and other advanced imaging tests are readily available at local referral practices. They are most useful when surgery is being considered for a bone tumor of the skull or spine, or when limb-sparing surgery is being considered for a tumor of the leg.
TREATMENT: GENERAL CONSIDERATIONS
Viewed from the perspective that a cure can rarely be achieved, all of the possible treatments available for bone cancer might be considered palliative.
Whenever one of our clients is interested in pursuing a cure, we are ready to provide guidance and treatment.
Euthanasia is the saddest treatment option; it is also likely to become, sooner or later in the course of the pet’s illness, the most reasonable and humane treatment option. (Bone cancer rarely produces complications that cause a pet to pass away without being euthanized.) Sometimes it is obvious that it is the right time for euthanasia: the pet’s pain may become unmanageable, or the pet might stop eating. Sometimes it is not so obvious: the owner, so tuned in to their pet’s behavior, might simply realize that its quality of life has become unacceptable. There is no certain amount of treatment that needs to be attempted before an owner decides the time for euthanasia is at hand; in some situations, little or no treatment is indicated. We will provide as much guidance as possible without taking the decision away from the owner.
AMPUTATION When the bone cancer involves a limb we can perform amputation to relieve pain. Combined with traditional chemotherapy, amputation is the treatment of choice when we are attempting to cure the patient. Most, but not all pets function well after amputation. We screen pets very carefully for possible contraindications and negative prognostic factors prior to this surgery.
LIMB-SPARING SURGERY Removal of a section of bone that includes the tumor without removing the entire limb is sometimes an option, depending on the location and extent of the cancer. Compared to amputation: limb-sparing surgery is more complicated; requires referral to a surgical specialist; survival times are similar but surgical complication rates are much higher. It is our opinion that, if limb-sparing surgery is to be attempted, it should be combined with radiation and/or chemotherapy.
SURGICAL REMOVAL WHEN THE TUMOR INVOLVES THE SKULL OR SPINE Complete removal of these tumors is often not possible. As with limb sparing surgery, it is our opinion that, if it is to be attempted, this surgery should be combined with radiation and/or chemotherapy.
CONVENTIONAL RADIATION THERAPY. Radiation can be used as a follow-up to surgery, or it can be used at a lower level on a less-frequent schedule (usually on an outpatient basis) to provide pain relief and decrease lameness. Radiation treatment for pets is not available in Maine; it requires trips to New Hampshire or Massachusetts.
STEREOTACTIC RADIATION TREATMENT With this specialized radiation treatment, large doses of radiation are delivered very precisely to the tumor. Survival times are similar to amputation. This treatment is even less-readily available than conventional radiation therapy, and it is much more expensive.
CONVENTIONAL CHEMOTHERAPY Conventional chemotherapy is the use of chemotherapy drugs in the well-known fashion. Typically multiple drugs are used, they are dosed to the maximum amount that the pet is likely to be able to tolerate, and they are given staggered throughout a cycle that is repeated multiple times. Pets generally tolerate chemotherapy better than people do, but side effects are still common. Conventional chemotherapy is used in addition to surgery and/or radiation in an attempt to achieve a cure; it is not used alone. It usually requires referral to a specialist.
METRONOMIC CHEMOTHERAPY This is not a particularly new therapy, but it has received increased attention and is increasing in use over the last several years. It involves administering traditional chemotherapy drugs at very low doses on a daily or every-other-day basis. They are administered in oral dose form at home by the pet’s owner. The cost is less, as is the risk of side effects. We can create a metronomic chemotherapy plan, so referral to a specialist is not necessary. (For more information, please see our YVCipedia article “Metronomic Chemotherapy” on our website, yarmouthvetcenter.com, or ask us to print or email you a copy.)
ANALGESIC MEDICATIONS Early in the course of the problem we can usually provide effective pain relief using one or two analgesics. As the problem progresses, we can often maintain this relief by adjusting doses and adding in one or two additional medications. NSAIDs (nonsteroidal anti-inflammatory drugs) are usually the first choice and are the cornerstone of analgesic therapy; also, they are usually part of our metronomic chemotherapy protocols.
OTHER MEDICATIONS Pamidronate is a medication that slows bone loss from tumor growth, and relieves pain in 30-40% of bone cancer patients. It is a relatively expensive intravenous medication that is administered once or twice monthly. A blood profile to assess kidney function is necessary prior to each dose.
Prednisone, the common corticosteriod medication, has various effects that make it useful for some bone cancer patients.
NUTRITIONAL SUPPLEMENTS Fish oil (omega 3 and 6 fatty acids) have anti-inflammatory and other effects that makes it a very worthwhile addition to the treatment plan for a pet with bone cancer. It is given as a daily supplement. Fish oil products vary widely in quality; to ensure good quality, we recommend using one of the veterinary products, Derma-3 Twist Caps or Welactin.
NUTRITION Hill’s, the manufacturer’s of Prescription Diet and Science Diet, make a complete and balanced canned dog food called N/D, for nutritional support of cancer patients. N/D provides high levels of protein and fat, arginine, and omega-3 fatty acids, and low levels of carbohydrates. This nutrient profile has the effects of depriving the cancer cells, but not the patient, of nutrition, and stimulating the patient’s immune system.
TREATMENT: OUR APPROACH TO PALLIATIVE THERAPY
PROGNOSIS: GENERAL CONSIDERATIONS
The vast majority of research on bone cancer in pets has been on osteosarcoma (OSA) in dogs, and the following prognostic details come from these studies. The prognosis for non-OSA bone cancer in dogs has not been studied extensively, but is very likely to be similar to that for OSA.
The prognosis for bone cancer in cats has not been studied extensively, but is generally considered to be better than that for dogs for bone tumors of the limbs, and about the same as that for dogs for tumors of the skull and spine.
The prognosis for bone cancer in pets other than dogs and cats is generally considered to be similar to that for dogs, but proportionally so, with respect to lifespan. For example, 1 year cancer survival for a dog with an average lifespan of 15 years would be 2 month survival in a rodent with an average lifespan of 2 years.
OSA of the head or spine (not including the mandible):
OSA of the mandible:
Nasal OSA, Digit OSA
Bone cancer of the skull and spine