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Understanding Osteosarcoma in Dogs

Osteosarcoma is a form of bone cancer in dogs that accounts for 85% of primary bone tumors diagnosed, making it the most common bone tumor. It is a highly aggressive tumor, characterized by local invasion and destruction of the bone as well as early metastasis (spread to other organs, the most common site of metastasis being the lungs). Osteosarcoma most commonly affects the limbs (or the appendicular skeleton) of large to giant breed dogs.  It can also occur in other bones such as the skull, ribs, vertebrae, and pelvis (the axial skeleton) which are more common sites in smaller dogs.

Clinical Signs of Osteosarcoma

The signs associated with bone cancer in dogs may be nonspecific and depend on the location. Tumors involving the limbs often cause various degrees of lameness, pain, and muscle wasting, and a firm swelling may become evident as the tumor grows. The pain can cause other problems such as irritability, aggression, loss of appetite, weight loss, whimpering, restlessness or reluctance to exercise.

Diagnosis and Work-up (Staging)

The initial evaluation for any dog suspected of having a bone tumor will include a complete physical exam, blood work (complete blood count, serum chemistry profile), urinalysis, radiographs of the primary site as well as the lungs, and an aspirate or biopsy of the lesion. In some cases a CT scan is recommended to evaluate for metastasis and/or surgical planning.  Unfortunately, 80-90% of dogs diagnosed with osteosarcoma already have microscopic spread to the lungs but we are not able to detect these microscopic lesions with X-rays or a CT scan. The work-up and staging are important for two reasons. First, it is necessary to determine the tumor type and extent of the cancer to determine the appropriate treatment and prognosis. Secondly, it also provides the clinician with information regarding your dog’s general health and may identify concurrent medical or musculoskeletal problems all of which may influence the treatment recommendations. 

Treatment Options for Osteosarcoma in Dogs

Treatment recommendations for bone tumors depend on multiple factors and the ultimate goal is to help improve your pet’s quality of life. Treatment can be divided into two parts:

  • Pain management/treatment of the primary tumor
  • Treatment to address the risk for metastatic disease

Pain Management

The initial focus of treatment is pain management. Osteosarcoma causes pain due to the invasion and destruction of normal bone by the tumor. There are several options for pain management depending on the location of the tumor. These include surgery (amputation for osteosarcoma of the limb), oral analgesics (pain relievers), radiation therapy and/or intravenous bisphosphonate therapy. 

For osteosarcoma involving a limb, amputation is the best method for pain control. It is much easier to control post-operative pain than it is to control chronic bone pain. An amputation also eliminates the risk of a fracture at the tumor site. Fractures occur because the tumor weakens the bone to the point that it can break. Fortunately, the risk of a fracture is low (~20%).  Most dogs will do very well with an amputation and often resume many of their normal activities such as running, playing, swimming, etc. It is important to understand that if an amputation is performed for osteosarcoma without chemotherapy, most patients develop metastatic disease and succumb to the cancer within 4-6 months, which is why we don’t always recommend amputation as a sole therapy.

For dogs that are not candidates for an amputation or situations in which a caretaker isn’t interested in amputation, we have several options for pain management that can be used singly or in combination. There is no “one size fits all” when it comes to pain management and we may need to try several combinations until we find what works best for a particular dog. 

Oral Analgesics include non-steroidal anti-inflammatory drugs (NSAIDS) (or aspirin-like drugs), steroids and narcotics. It is common to combine a NSAID with a pain medication like gabapentin, amantadine, codeine and fentanyl.

Palliative Radiation Therapy (PRT) involves the use of several large doses of radiation administered once a week, for 3-4 doses. PRT appears to be the best option for pain management if surgery (amputation) is not pursued. The goal of this form of radiation is to improve/maintain the patient’s quality of life with minimal negative impact (minimal side effects). Approximately 70% of dogs experience pain relief with PRT which lasts for an average of 4 months. It may be possible to repeat a course of PRT, depending on the dog, though the duration of the response is usually shorter than the original response. PRT for bone tumors (appendicular) is for pain management and is not a treatment for the primary tumor. In most patients the tumor continues to progress even though the patient is more comfortable and fracture is still a risk.

Bisphosphonates: Bisphosphonatesare a class of drugs that are meant to slow or prevent bone breakdown as well as increase bone production. This class of drugs is used frequently in women to prevent osteoporosis (ie. Boniva or Fosamax). Several of the drugs have also been used to help control pain from bone destruction. The most commonly used drug is zoledronate. This medication is administered intravenously once every 4 weeks as a 15 minute infusion. Initially we plan 2-3 treatments and then determine if there has been an improvement. If there has been an improvement, this drug can be repeated for as long as there is response and the patient tolerates the drug. Side effects are rare, but we do monitor kidney function prior to each treatment due to a low risk for kidney damage.

Chemotherapy

The most common cause of death in dogs with appendicular osteosarcoma, especially those undergoing an amputation, is metastasis to the lungs. Because of this, systemic chemotherapy is recommended as a follow-up to surgery for dogs with appendicular osteosarcoma. Chemotherapy is not likely to cure most dogs with osteosarcoma but can significantly prolong their quality of life to 10-12 months on average with 20% of patients alive at 2 years. Survival time for dogs treated with an amputation alone is about four months. We currently recommend the chemotherapy drug Carboplatin. This chemotherapy agent is administered intravenously once every three weeks for 6 doses. Most dogs tolerate chemotherapy well with less than 10% experiencing side effects significant enough to warrant an outpatient visit and less than 1% will require hospitalization or experience any life-threatening side effects secondary to chemotherapy.  

The goal of any treatment is to maintain your pet’s quality of life. Your oncologist will work with you to determine the best course of treatment for you and your dog.

Canine Splenic Hemangiosarcoma: Spleen Cancer in Dogs

Hemangiosarcoma of the spleen, or spleen cancer in dogs, is a cancer that is diagnosed in many canines every year. It is a cancer made up of the cells that line blood vessels, and therefore can be found in any part of the body. However, the most common sites include the spleen, liver and right auricle of the heart. Approximately 2/3rds of masses in the spleen are malignant and of those, 2/3rds are diagnosed as hemangiosarcomas. Splenic hemangiosarcoma is most often diagnosed in older dogs, with German Shepherds, Labrador Retrievers and Golden Retrievers being the most commonly affected breeds.

Splenic hemangiosarcoma is very dangerous because there are very few signs of the cancer until the spleen either ruptures or the cancer happens to be spotted on a routine abdominal radiograph or ultrasound. This is largely due to the fact that the spleen is deeply seated in the body. In fact, many dogs that are diagnosed with splenic hemangiosarcoma present to their veterinarian on an emergent basis with a history of lethargy, decreased appetite, weight loss, acute collapse, pale to white mucous membranes and/or swelling in their abdomen. Vomiting and diarrhea can also be seen in a small percentage of patients.

Splenic masses can sometimes be seen with abdominal radiographs but are most often diagnosed with an abdominal ultrasound. In either case, once a splenic mass has been detected, it is in the patient’s best interest to undergo further diagnostics (i.e. staging tests) to evaluate for any evidence of metastasis (spread of the cancer to other areas of the body). These tests include an abdominal ultrasound (if not already performed) to evaluate for possible disease in any of the other abdominal organs, chest radiographs determine if there is any evidence of disease in the lungs, blood work that includes a CBC (which checks the red and white blood cells and platelets), a chemistry panel, clotting times and a urinalysis. An echocardiogram of the heart may also be warranted. Studies have shown that a small percentage of patients with splenic hemangiosarcoma can have a mass in the right auricle of the heart at the time of diagnosis.

Surgery is the primary treatment for a splenic mass and we need to keep in mind that not all splenic masses are malignant. The only way to obtain a definitive diagnosis is with removal of the spleen and submitting the sample for biopsy.  The hope is to pursue surgery before the mass or masses rupture, but most patients present in a crisis secondary to rupture of the mass leading to emergency surgery. With surgery alone, the median survival time is approximately 1-2 months with patients succumbing to metastatic disease.

Hemangiosarcoma has a high metastatic potential even if the spleen has been removed. Due to the aggressive nature of hemangiosarcomas, chemotherapy may be recommended to try and slow the progression of the cancer.  The primary chemotherapy drug used to treat hemangiosarcoma is doxorubicin (also known as adriamycin). Fortunately, most patients tolerate chemotherapy well with minimal side effects. These side effects can include stomach upset (decrease in appetite, nausea, vomiting, diarrhea and lethargy), decrease in white blood cell count and thinning of the fur coat. In addition, doxorubicin has also been shown to have a cumulative toxicity on the heart and because of this, doxorubicin has a lifetime dose in dogs that we do not exceed. In some cases, an echocardiogram may be recommended prior to the first treatment to obtain a baseline of their heart function and then again prior to the 5th or 6th treatment. Doxorubicin is administered intravenously once every 3 weeks for 4-6 treatments. Patients treated with surgery and chemotherapy experience a median survival time of 4-6 months.

In addition to traditional therapy, there are a couple of other treatment options that have shown some promise, but there is limited information regarding their true efficacy. These include I’m Yunity and Yunnan Baiyao. I’m Yunity is an extract of polysaccharopeptide from Coriolus versicolor mushroom (commonly known as the Yunzhi mushroom) that showed some promise in a small study out of the University of Pennsylvania. This study was very small, so it is unknown whether the information gathered in this study is representative of the larger population.

Many oncologists are prescribing the Chinese supplement Yunnan Baiyao. This supplement is thought to help slow down or stop bleeding from some of the cancerous lesions. There is also some data that shows it may also promote healing and possibly has some anti-tumor benefit against hemangiosarcoma. To better understand the benefit of this supplement, clinical studies are needed.

There may be some ongoing clinical trials available to your pet. Clinical trials are most often trying to find a new and possibly better treatment to improve the outcome for dogs with hemangiosarcomas.

Splenic hemangiosarcoma is a very aggressive cancer and, unfortunately, long-term control/survival is difficult to achieve.  Our main goal when treating your pet is to provide good quality time for all of you.

Common Signs of Cancer in Pets

Common Signs of Cancer in Pets

Common Signs of Cancer in Pets: A Great Dane Looks Outside Through a Window

Treating cancer in pets is a large part of what we do here at AVIM&O. An estimated 4 million dogs and cats will develop cancer each year. As dogs get older, their risk of cancer increases. Almost half of dogs over the age of 10 will develop cancer, while there is less information regarding the cancer rate in cats. Still, we do know that cancer is the leading cause of death in 47% of dogs and 32% of cats.

A Morris Animal Foundation study found that 41% of animal owners feel that cancer is the biggest health concern for their pet. It is very difficult to detect cancer early in pets, and unfortunately in most cases, cancer cannot be detected with routine blood work.

However, according to the American Veterinary Medical Association, there are 10 things you can look for. These signs are not definitive for a cancer diagnosis, but they may be able to detect another medical condition early that might require additional veterinary attention and/or treatment. Early detection is key when dealing with cancer, so learn to spot the signs discussed here:

  • Abdominal swelling. This can be a slow or quick onset and it is important to see your veterinarian to try and determine a cause. The work up for this usually starts with blood work, a urine sample, and an abdominal ultrasound.
  • Bleeding from the mouth, nose, or other parts of the body. Melanoma is the most common oral tumor in dogs, and squamous cell carcinoma is the most common oral tumor in cats. Seeing your local veterinarian twice a year for routine examinations can help to identify these tumors sooner. Early detection of these tumors has shown to result in an improved outcome. So if you notice your pet has blood-tinged saliva, is eating slower, has colored discharge from the nose or bleeding from any other areas of the body, the best thing is to have them evaluated by your veterinarian. In most cases some additional testing will be recommended to try and determine a cause and diagnosis.
  • Difficulty breathing. Any time there is a concern that your pet is having difficulty breathing, they should be evaluated immediately either at your local veterinarian or the closest emergency clinic. Evaluation with blood work and radiographs of the chest will likely be recommended as a starting point to try and determine a cause.
  • Difficulty eating or swallowing. This could be a sign of dental disease or something more serious and warrants a visit to your local veterinarian for further evaluation.
  • Lumps, bumps or discolored skin. Any new mass found on your pet should be aspirated by your local veterinarian to determine whether additional steps should be pursued. After the aspirate, a next step may include taking a small biopsy sample (called an incisional biopsy) to gain a better understanding of the mass vs. complete excision if the aspiration reveals that the mass is a concern. As dogs get older they can develop new masses like lipomas (fatty masses), which are benign. Any new masses should be evaluated so your local veterinarian can help guide you towards the best treatment options available. In some cases, monitoring may be the best treatment option, but only after you determine what the condition is.
  • Non-healing wounds. Most cuts and scrapes will heal on their own. Unfortunately, if your pet has a sore that is not improving after a few days to a week, they should be seen by your local veterinarian. Cancer is able to do a lot of things, but it cannot heal and usually continues to grow. Getting to a malignant tumor sooner allows the doctor to provide more treatment options and improve the outcome for most pets.
  • Persistent diarrhea or vomiting. Dehydration can occur quickly, even if your pet is still drinking. If they have had more than 3-4 vomiting episodes in a day or more than 36 hours of diarrhea, then they should be seen by your local veterinarian. The sooner they are seen the lower the chances are that they will require hospitalization. Tests that will be recommended usually include: blood work, analysis of urine, X-rays, and possible ultrasound. There are many benign causes of vomiting and/or diarrhea, but cancer is always a concern and should be ruled out as a possible cause.
  • Sudden or chronic changes in weight. If you notice that your pet has had an unexplained drop in their weight, they should see their veterinarian immediately. Weight loss is sometimes one of the first indicators of a cancer diagnosis. The first steps are very similar to what has already been stated and usually include blood work, a urine sample, radiographs and/or an abdominal ultrasound.
  • Unexplained swelling, heat, pain or lameness. There are a lot of different causes for these signs in dogs and cats. Any persistent swelling, pain or lameness that does not improve with supportive care should be investigated further. In dogs, a bone tumor called osteosarcoma can cause a firm swelling in either their front or back legs, but rarely in other bones in the body. Most of these dogs will improve initially with pain medications and anti-inflammatories, but it never completely resolves and the swelling remains. If this is the case, then along with initial diagnostics (i.e. blood work and a urine sample), radiographs of the affected limb are recommended. If there are changes noted in the bone, the next steps usually include chest radiographs and either an aspirate and/or biopsy with culture of the concerning area in the bone to try and arrive at a diagnosis.
  • Visible mass/tumor. As stated above under lumps, bumps or discolored skin, any new mass should be evaluated with aspiration. Based on the aspirate results, further recommendations can be made.

If your pet is diagnosed with cancer, the next step is being referred to an oncologist where they will discuss your pet’s prognosis and treatment options with you. Fortunately, dogs and cats tolerate most cancer treatments very well. The goal with any cancer treatment is to ensure that your pet maintains a good quality of life before, during, and after treatment. However, in many instances a cure is not possible. In these cases, our goal is to achieve a good quality of life for your pet for as long as possible. We believe quantity of life is meaningless without quality. It is also important to realize that you know your pet best, and the criteria for determining one animal’s quality of life may not suit another. Being armed with the correct information allows you to be the best advocate for your pet.