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.
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.
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.
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 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 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.
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.