Overview of Treatments

Depending upon the grade, stage and type of cancer, your team will recommend one or a combination of treatment options. Multiple treatment options that combine surgery, radiation and chemotherapy are the rule rather than the exception. This is because the treatment of cancer in animals has become as sophisticated and successful as the treatment of cancer in humans.


Chemotherapy is used to treat cancer at the tumor site, as well as the cancer that may have spread through the body. Most chemotherapeutic drugs act directly on cancer cells, preventing them from maturing or reproducing. Unlike humans, the side effects of chemotherapy in pets are relatively mild. Doses of drugs and treatment schedules are calculated to minimize discomfort to the pet, while providing the most effective defense against the cancer. As a result, most people are surprised at how well their pets feel while undergoing chemotherapy. The goal is to kill and slow the growth of cancer cells, while producing minimal negative effects on normal cells. If your pet requires a plan of chemotherapy, your veterinarian will most likely bring in a specialist (an oncologist) to develop the plan of attack and administer the treatments. In addition to the latest and best medical treatments, an oncologist will provide the specialized equipment and supervision that your pet needs. Chemotherapy protocols are frequently changed or customized to achieve the best outcome for your pet.

Under what conditions is Chemotherapy used?
Chemotherapy is a systemic therapy, meaning it works throughout the body--as opposed to radiation therapy which is a local or regional therapy. Chemotherapy is used when a cancer or tumor has already spread (or metastasized) or when there is a high risk of the tumor spreading.

Which tumors are commonly treated with Chemotherapy?
Many types of cancers are treated with chemotherapy. The most common tumor being lymphoma, a systemic cancer of part of the immune system. Osteosarcoma (bone cancer) and hemangiosarcoma are both treated with chemotherapy because of the very high likelihood of metastasis (spreading), even after the tumor is removed. Many other types of cancers such as mast cell tumors, mammary gland tumors, bladder cancer, and many others are often treated with chemotherapy.

How is Chemotherapy administered?
Chemotherapy can be administered orally in the form of a pill or injected into a vein (intravenous), into a body cavity (such as the chest or bladder), into a muscle (intramuscular), or into the spinal fluid (intrathecal). Currently, most chemotherapy is administered intravenously; however, oral chemotherapy drugs are gaining wider use.

Are there any side effects?
Chemotherapy in pets is very different from chemotherapy in people. We use much lower doses of chemotherapy and spread the treatments out over a much longer period of time. This is done to try and allow us to treat your pet's cancer effectively without causing the side effects that occur in people. In addition, there have been tremendous advances in medications that are used to prevent the common side effects of chemotherapy-vomiting, diarrhea and loss of appetite. Cerenia is a relatively new drug and it is quite effective at preventing or stopping nausea and vomiting. There are also regimens that we have developed that dramatically reduce the side effects of diarrhea and loss of appetite. We are as concerned as you are about maintaining the highest quality of life for your pet-both during and after treatment.

How Should I prepare for treatment?
Most chemotherapy is given in an outpatient setting, typically over a 5-45 minute time period. Some chemotherapy is given slowly over a few hours, but our team will alert you when this is needed. Most animals do not need to be fasted before chemotherapy, but we will make recommendations based upon your pet's unique circumstances.

What should I expect after treatment?
Most pets-80-90%- have no or minimal side effects after chemotherapy. Vomiting, diarrhea, loss of appetite and loss of energy are the four most common side effects, but if these do occur they are usually mild. Your oncologist will discuss ways of preventing these side effects, as we have found that it is easier to prevent them than it is to treat them once they begin. Greater than 95% of our clients were pleased with how their pets handled therapy at our practice and would do it again.

Radiation Therapy

In veterinary medicine, radiation therapy was first attempted at the beginning of the twentieth century. During the past 50 years, major advances have been made. The use of histopathology, MRI, and CT scans has resulted in more accurate diagnosis of the type and location of tumors. Newer radiation equipment and new technology such as intensity modulated radiation therapy (IMRT) has allowed the radiation to be tailored to the individual patient's tumor with more and more accuracy, so that normal tissues around the tumor can be spared. This has increased the effectiveness and decreased the side effects and risks of radiation therapy.

Under what conditions is radiation therapy used?
Radiation therapy can be used alone or in combination with surgery and/or chemotherapy to provide long term control or death of a tumor. It is used for tumors that have not spread to other sites in the body and offers a potential cure for some localized tumors. In other cases, radiation therapy can be used for its palliative effect (relieving pain or other signs of disease). Even if the tumor cannot be destroyed, radiation may result in rapid pain relief and may shrink the tumor or slow down tumor growth. This often will improve the quality of life of the animal.

Which tumors are commonly treated with radiation therapy?
Tumors that are commonly treated with radiation include oral tumors, nasal tumors, brain tumors, nasal tumors, mast cell tumors, soft tissue sarcomas, bone tumors and many more. However, radiation can be used to treat almost any localized tumor and it is sometimes used to treat widespread tumors. Radiation can often be an effective treatment for tumors when surgery either is not possible because it will be too dangerous. For example, tumors in certain locations in the brain may best be treated with radiation alone.

Many times radiation will be used after surgery if the tumor cannot be removed completely with surgery. This is commonly done for soft tissue sarcomas, mast cell tumors and other superficial tumors in areas where the tumor cannot be fully removed.

How is radiation administered?
If your pet is a candidate for radiation and you decide to go ahead with treatment, your oncologist/radiation oncologist will talk to you about how many treatments your pet will need and the side effects that you should expect. Sometimes a CT scan will be needed to plan the radiation, even if your pet has had an MRI or CT scan already. This scan is done with your pet in a positioning device that will be used for each future treatment. The scan is then used to develop a radiation plan that is customized for your pet's specific tumor, to treat your pet effectively with as few side effects as possible.

For each treatment your pet will need to be placed under general anesthesia to make sure that they stay perfectly still for the treatment. Although there is always a risk any time an animal is placed under anesthesia, the anesthesia for radiation is typically very short and very short acting drugs are used, so potential complications are rare.

Are there any side effects?
Side effects of radiation for your pet will depend upon the dose of radiation used to treat the tumor and also the type of radiation that is used. With daily, definitive treatments the normal tissues around the tumor will often develop redness and irritation. Sometimes this can cause significant discomfort for your pet. Newer radiation technology allows us to minimize these side effects in most patients. However, pets who are likely to develop significant side effects will often require pain medications or anti-inflammatory medications. Your oncologist/radiation oncologist and your regular veterinarian will work as a team to keep your pet as comfortable as possible. These side effects are almost always temporary and the goal in these situations is to get your pet through the side effects and back to having a normal or improved quality of life after the treatment. Often there can also be a risk of a long-term, permanent side effect from radiation. Fortunately these side effects are rare and your oncologist/radiation oncologist will discuss these with you before starting treatment.

How Should I prepare for treatment?
Usually your pet will need to have food and water taken away the night before each treatment, but your doctor will confirm this with you to make sure that it is safe to do this. If your pet gets groomed on a regular basis it may be a good idea to have them groomed prior to radiation. Once the radiation starts you may not be able to have your pet bathed or groomed because there will be marks on their skin that cannot be removed.

What should I expect after treatment?
Following radiation therapy side effects may progress for up to two weeks if your pet develops side effects. Your oncologist/radiation oncologist will work with you and your pets regular veterinarian to manage your pets comfort level and managing their medications. A recheck exam is typically recommended in one to two weeks to make sure that the healing process is going well. Your pet also should have routine recheck exams to monitor for regrowth of the tumor or for late side effects from the radiation. A plan will be set up to have these done at The VCC or with your pet's regular veterinarian.  

Intensity Modulated Radiation Therapy (IMRT)

Intensity Modulated Radiation Therapy or IMRT may be used to treat your pet's tumor. This is a relatively new type of treatment that uses multiple, complex beams of radiation to shape the radiation dose to your pets tumor. By pinpointing the radiation to the tumor it minimizes the amount of radiation that is given to your pet's normal tissues. This will usually minimize the potential side effects for your pet. Many times this is done as part of a definitive radiation treatment using the same number of treatments, but it also can be done as part of a treatment known as stereotactic radiation or stereotactic radiation. This involves a small number of treatments contoured to your pet's tumor. This is a very effective way to deliver high doses of radiation to certain tumors.

Half Body Radiation

Most dogs with lymphoma will go into remission after only a few treatments and they will often stay in remission for months.  During this time, aside from having to come to see the oncologist for treatment, their quality of life is often very good.  Once they get into remission owners often report that they are running, playing or just living their normal life as if they never had cancer. Unfortunately, almost all of these pets will eventually come out of remission and succumb to their disease.  In the past twenty years there has been little to no improvement in the remission and survival times with chemotherapy alone. With this protocol, dogs are first treated with chemotherapy to get them into remission and this is followed by two treatments of half body radiation.  Then a low dose rate is used, meaning that dogs develop almost no side effects from the treatment.  They can get some changes to their hair coat and some intestinal upset, but otherwise they are typically fine.  Most dogs will then go on to complete a shortened chemotherapy protocol.  Initial results suggest that by combining radiation therapy with chemotherapy in this way dogs are in remission longer and are living longer with lymphoma.

Strontium – 90

Strontium – 90 probes have been used to treat small superficial tumors, including mast cell tumors in cats, solar induced squamous cell carcinomas in cats, small mast cell tumors in some dogs like pugs.  It may be beneficial in palliative treatment of squamous cell carcinoma under the tongue in cats.  It is great for treating pets with multiple tumors, because each treatment is usually less than ten minutes, and requires only a short anesthetic episode.  For pets with multiple tumors it allows us to treat all of their tumors in one, shorter anesthesia.  Also, it can be very helpful for treating eyelid tumors or corneal tumors, which are often very difficult to remove with surgery.

Targeted Therapy

Targeted cancer therapies refer to drugs or other agents that block the growth and/or spread of cancer by interfering with specific molecules in the tumor cells known to be important for cancer progression. Scientists often call these molecules “molecular targets” so targeted cancer therapies are sometimes referred to as “molecularly targeted drugs,” “molecularly targeted therapies,” or other similar names. Since targeted therapies act on molecules specific to cancer cells, they hold the promise to be more effective than other types of treatment, including chemotherapy and radiation therapy, with potentially less toxicities. In some cases, targeted therapies can be combined with existing treatments in order to improve the efficacy.

How do targeted cancer therapies work?

Targeted cancer therapies interfere with cancer cell division (multiplication) and spread to other organs (metastasis) in different ways. Many of targeted therapies focus on proteins involved in signaling pathways, which form a complex communication system that cells use to control basic cellular functions such as cell division, cell movement or how a cell responds to specific external stimuli. Since targeted therapies are designed to block signals that tell cancer cells to grow and multiply, these therapies help stop cancer progression and may cause killing of cancer cells through a process known as apoptosis. Other targeted therapies can cause cancer cell death directly, by specifically inducing the process of apoptosis, or indirectly, by stimulating the immune system to recognize and destroy cancer cells and/or by delivering toxic substances to them.

Once a molecular target has been identified by scientists, a therapy must be developed. Most targeted therapies are either small molecule drugs or monoclonal antibodies. Small molecule drugs are typically able to diffuse into cells and can act on targets that are found inside the cell. Most monoclonal antibodies usually cannot diffuse into the cells and are directed against targets located on the outside cell surface. Candidates for small-molecule drugs are usually identified in studies known as drug screens - laboratory tests that look at the effects of thousands of test compounds on a specific molecular target. The best candidates are then chemically modified to produce numerous versions, each of which is tested to identify the most effective and specific drug(s) - called lead compound(s). The lead compound is then tested in laboratory animals for safety and any signs of efficacy, and once these tests are satisfactorily completed, the lead compound becomes available for a clinical trial in client-owned pets with the disease of interest. If the drug shows efficacy in these client-owned pets and has an acceptable safety profile, the drug's safety and efficacy data is submitted for a review by government regulatory agencies that oversee the development of drugs for veterinary medicine. Once approved, the drug becomes commercially available. 

What targeted therapies are currently approved in cats and dogs with cancer?

In the United States, two targeted cancer therapies are currently approved for mast cell tumors in dogs. Palladia (toceranib, Pfizer Animal Health) is currently approved for Grade II/III cutaneous (skin) mast cell tumors in dogs; and Kinavet (masitinib, AB Science) has been recently approved as treatment for recurrent or non-resectable (tumors that cannot be surgically removed) Grade II and Grade III cutaneous mast cell tumors in dogs that have not previously received radiotherapy and/or chemotherapy except corticosteroids.