INTRODUCTION

Bone cancer is a relatively common type of cancer in dogs, and a less common type in cats and other pet species.

We see cases of bone cancer can that are 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. While bone cancer is somewhat less common in other pet species, osteosarcoma is still the most common type of primary bone cancer in non-canine pets.

Unfortunately bone cancer is almost always malignant, meaning it is aggressive and carries a poor prognosis. Metastasis (spread to other body parts) is common and seen often in the lungs and bones other than the one that contains the primary tumor. By the time bone cancer is diagnosed it is extremely likely that it has already metastasized even if diagnostic tests do not reveal this.

DIAGNOSIS

PHYSICAL EXAM

Swelling and pain at the tumor site are the most common findings. Additionally, when the cancer occurs in a leg there is usually a persistent lameness. When the cancer occurs in the skull or spine there might be a bulging eye, nasal discharge, difficulty eating and drinking, drooling, or neurologic problems. When metastasis has occurred, the pet may be lethargic and have a decreased appetite. Any of these symptoms, including swelling of the tumor, can appear suddenly and progress quickly or slowly. This truly is a cancer that does whatever it wants.

With primary bone tumors, 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 somewhat 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.

Of special note: it can be very difficult to obtain a diagnostic biopsy by removing a small piece of bone from a possible 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.

When bone cancer involves a leg we have to consider the treatment option of amputation (see below). Amputation allows us to have the entire tumor as a biopsy, acting as both treatment and diagnostic tool. We can be very certain that a bone problem is a tumor based on x-rays, so proceeding to amputation without a smaller biopsy sample is a very reasonable option. And when the bone problem is something other than a tumor, the small range of possibilities includes only problems for which amputation is also a very appropriate treatment, so, from that perspective, this surgery is a very reasonable choice.

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. We consider a part of their full work up and staging of the disease. Also, abnormally elevated levels of a couple of tests on a general profile can help inform prognosis.

ULTRASOUND EXAM

Abdominal organs and other soft tissues are not common sites for metastasis of bone tumors in dogs but we will sometimes recommend this as a part of the full work up and staging of the disease. Spread to these organs are somewhat more common sites in cats and other pets.

ADVANCED IMAGING

We have CT scans available by referral. Again, depending on the case this may be a recommended step in the full work up and staging of the disease. This advanced imaging is most useful when surgery is being considered for a bone tumor of the skull, pelvis or spine, or when limb-sparing surgery is being considered for a tumor of the leg.

TREATMENT

GENERAL CONSIDERATIONS

Faced with a diagnosis of bone cancer and the poor prognosis that comes along with it, some of our clients express their desire to pursue a course of treatment that will keep their pet comfortable for as long as possible, without “putting them through too much,” and/or without incurring significant expenses. This is palliative care: treatment with the goal of alleviating symptoms but not obtaining a cure by eliminating the cause of the problem.

Viewed from the perspective that a cure can rarely be achieved, all of the possible treatments available,for bone cancer might be considered palliative. That said, 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.

Ultimately we create an individual treatment plan for each pet using some combination of some of the following options. Bone cancer of the limb of cats, with no detectable metastasis, is an exception; amputation with no additional treatment yields a prognosis as good as when additional treatment is used.

AMPUTATION

When bone cancer involves a limb we most commonly recommend and pursue amputation. The primary goal of amputation is to relieve pain. Bone cancer is persistently painful and sometimes the pain cannot be managed well with medication alone. Amputation is certainly a major operation that requires considerable recovery time, but most patients have recovered from the post-operative pain within 2 weeks. (Post-operative mobility is a greater concern, and is the reason the decision on whether or not to amputate must be very carefully considered.) While it is a difficult option for a pet owner to contemplate, it is the single-most useful treatment option we have for many bone cancer patients.

Combined with traditional chemotherapy, amputation is the treatment of choice when we are attempting to cure the patient. (Again, the chance of achieving a cure is very slim, even with this combination of treatments.)

Not all pets function well after amputation. We screen pets very carefully for possible contraindications and negative prognostic factors prior to this surgery. Please see our article about amputation for additional information.

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; typically requires referral to a surgical specialist; and survival times are similar to amputation but surgical complication rates are much higher. It is our opinion that, if limb-sparing surgery is to be attempted, it must be combined with radiation and/or chemotherapy.

SURGICAL REMOVAL WHEN THE TUMOR INVOLVES THE SKULL, PELVIS OR SPINE

Complete removal of tumors in these locations is usually 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.

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, NSAIDS are usually part of our metronomic chemotherapy protocols.

OTHER MEDICATIONS

Pamidronate is a medication that slows bone loss from tumor growth, and is used to relieve pain in bone cancer patients (it is not a chemotherapy agent). It is effective at relieving pain in 30 to 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) has 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, or feeding prescription diet J/D.

NUTRITION

Hill’s, the manufacturer’s of Prescription Diet and Science Diet, make a complete and balanced canned dog food called ONC Care, 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.

OUR APPROACH TO PALLIATIVE THERAPY

When an owner is interested in pursuing palliative care, we believe one approach worth considering is combining metronomic chemotherapy with analgesic therapy and fish oil. With the exceptions of conventional chemotherapy and stereotactic radiation therapy, which would only be used if a cure was attempted, any or all of the other treatment options could be added to this base of palliative care. We work with the owners to create a treatment plan that is right for their pet.

PROGNOSIS

GENERAL CONSIDERATIONS

Unfortunately, the long term prognosis for any type of bone cancer, with any type of treatment, is poor. The short term prognosis (weeks to months) is fair for maintaining a good quality of life.

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.

PROGNOSIS: DOGS

• OSA of the limbs:

  • Amputation alone

    • 4 to 5 month average survival

    • 1 year survival rate 10%, 2 year 2%

  • Amputation, limb-sparing surgery or stereotactic radiation therapy combined with platinum based chemotherapy

    • 10 to 12 months average survival

    • 2 year survival rate 15% to 25%

  • Amputation, limb-sparing or stereotactic radiation therapy combined with conventional chemotherapy

    • 8 months average survival

    • 1 year survival rate 35%, 2 year survival rate 17%

  • Prognosis worse if the tumor is in the upper front leg near the shoulder

  • Prognosis worse if alkaline phosphatase (a test in the general blood profile) is elevated

  • Palliative care without surgery or metronomic chemotherapy

    • Survival time up to 4 to 5 months

    • Depends on how successful pain control is

  • Once metastatic disease is apparent survival times usually less than 2-3 months regardless of treatment

• OSA of the head or spine (not including the mandible):

  • Prognosis similar or worse compared to OA of the limb

  • Depends mostly on whether primary tumor can be completely removed

• OSA of the mandible:

  • Better prognosis than the rest of the head or spine

  • 60% metastasis rate (versus almost 100% for OSA in other locations)

  • Average survival 17 months with mandibulectomy

  • Addition of chemotherapy of uncertain value

• Nasal OSA, Digit OSA

  • Prognosis similar to OSA of the limb

PROGNOSIS: CATS

• Bone cancer of the limbs

  • Amputation alone greater than two years

  • Amputation with chemotherapy or radiation unknown, but considered not to be better than amputation alone

• Bone cancer of the skull and spine

  • Surgery alone average 5.5 months

  • Surgery with chemotherapy or radiation unknown, but considered to be worth considering