A Deep Dive Into Cancer Treatment Options
By FidoCure's Dorothy Jackson Girimonte, DVM, DACVIM (Oncology), CVA

There are many therapy options available to treat cancer in our companion animals. These include surgery, radiation therapy, chemotherapy, immunotherapy, and targeted therapy. Veterinary cancer patients, as in people, are often treated with a combination of these therapies.

Is there a cure?
Despite treatment, many of our patients are not able to be cured for several reasons. One is the aggressive nature of various cancers in our companion animals. They can develop and progress very quickly. Another reason for this progression is the faster metabolism of our patients; this is why their lifespans are shorter. Compared to people, we treat our patients with a lower dose of chemotherapy. This, unfortunately, is why we rarely cure them. However, these lower doses allow us to ensure our patients have a good quality of life while undergoing therapy.

Surgery is defined as the physical removal of organs and tissues to treat varying diseases. In veterinary medicine, there are several surgical procedures including biopsy, resection for cure, palliation of symptoms, and debulking.

Biopsy is the procedure by which a piece of tissue is obtained for microscopic analysis (histopathology). This analysis can not only provide a diagnosis but may also provide more information about the nature of the cancer (referred to as grade).

There are several reasons to obtain a pretreatment biopsy: fine-needle aspiration is not diagnostic, type and/or extent of treatment would change based on the tumor type or grade, knowledge of the tumor type or grade would change whether or not curative-intent treatment would be pursued.

Dig Deeper:

It is said that the first surgery is the best chance to achieve a “cure”. Prior to surgery, imaging may be recommended so that an appropriate treatment plan can be established. Advanced imaging, like CT scan, has enhanced our ability to assess the extent of various cancers and plan an approach that gives the best chance of long-term control (ie prevent recurrence).

Palliative surgery is used not to prolong survival but to improve a patient’s quality of life (pain relief, improved function). There are many careful considerations to make sure that any expected morbidity does not outweigh the potential benefits for the patient. One example of palliative surgery is removing a painful, infected mammary mass in a patient that is not symptomatic for their metastatic lung disease.

Debulking or cytoreductive surgery is the incomplete removal of a tumor. This procedure is indicated in order to enhance the efficacy of other treatment modalities, like radiation therapy and chemotherapy.

Radiation Therapy
Radiation therapy, also known as radiotherapy, is the use of ionizing radiation to control or kill cancerous cells. It can be used as the sole treatment or combined with other therapies. If a tumor is excised incompletely with surgery, radiation can be used to kill the remaining disease. Radiation can also be used to slow the growth of a mass or for palliative pain relief. There are two forms of radiation: definitive and palliative.

AAHA - Radiation Therapy
Definitive radiation delivers lower doses of radiation often daily on a Monday-Friday basis for 3-4 weeks. It is commonly used following surgery when there is microscopic disease present. Its intent is to hopefully obtain better control of the disease and delay, if not prevent, recurrence. Side effects are reported but often mild and well controlled with anti-inflammatory and pain medications. The risk of side effects has decreased with the new modalities of image-guided radiation therapy and stereotactic radiation therapy.

Dig Deeper:

Palliative Radiation
Palliative radiation therapy uses higher doses of radiation administered once to twice weekly for 4-6 doses total. It is used when there is bulky disease with the hope of slowing down tumor growth. It can also be used in bone tumors to help with pain relief. Side effects are not as common compared to definitive radiation therapy. Even though higher doses are used, any normal tissues affected have time to repair before the next treatment.

Chemotherapy is a type of cancer treatment that uses anti-cancer drugs to kill cancerous cells. Cytotoxic chemotherapy drugs target cancer cells because they are rapidly dividing and interfere with their further division and continued growth.

Chemotherapy can be used for a variety of reasons. It can be used following surgery and/or radiation to prevent further metastasis (spread of disease elsewhere). It can be used as the sole therapy to slow down disease progression, especially when the cancer is not amenable to other modalities. There is even evidence that some chemotherapy agents can sensitize cancer cells to radiation, so they are given in conjunction with radiation treatment.

Our goal in veterinary oncology is to balance the benefits of chemotherapy in controlling the disease with the risks of side effects. Because cytotoxic chemotherapy targets rapidly dividing cells, normal tissues that have a faster growth rate can sometimes be mistaken for cancer. The normal tissues that may be affected include the bone marrow (immune system), gastrointestinal tract, and fur.

If the bone marrow is affected, this is typically seen as a decrease in normal cell counts, including the red blood cells, white blood cells, and platelets. A marked decrease in the white blood cells is of importance, as it can predispose these patients to secondary infections. Gastrointestinal side effects can include decreased appetite, vomiting, and diarrhea/soft stools. These are often easily treated with oral medications and supportive care.

We do not see hair loss as commonly as we do in people because of the differences in hair growth and turnover. The breeds most commonly affected with loss of fur are those that require grooming on a regular basis (ie poodles, maltese, cocker spaniels). Other breeds may shed more but not lose their fur completely.

Immunotherapy is the treatment of cancer by using the body’s own immune system. The main role of the immune system is to recognize foreign proteins and rid the body of them. We now know that cells whose main function is to prevent uncontrolled immune responses also serve to block the natural immune response against tumors.

One of the major goals of immunotherapy is to develop a strong, long-lasting antitumor response without causing adverse side effects. One example of immunotherapy used in veterinary medicine is the Oncept melanoma vaccine. It is not a preventative vaccine but instead is given once a diagnosis of melanoma has been made. Its objective is to stimulate the immune system to attack melanocytes, including the malignant melanoma cancer cells.

Dig Deeper:

As we learn more about the immune system and its role in regulating and preventing cancer, we will be able to develop more immunotherapies for our companion animals.

Targeted Therapy
Targeted therapy attacks cancer cells based on a mutation they carry. This form of precision medicine is widely used in people. A person’s tumor is sequenced in order to determine what mutations are present that could be driving the cancer progression. Chemotherapy that has been developed to target those specific mutations is then used either as the sole treatment or in combination with other treatment modalities.

Now that we have sequenced the canine genome, we at FidoCure are researching the use of targeted chemotherapy drugs to treat canine cancer. Palladia (toceranib) is currently the only veterinary-approved targeted chemotherapy for use in dogs. It was developed to treat canine mast cell disease, as this disease commonly carries the c-kit and other tyrosine kinase mutations.

At FidoCure we are providing new hope for canine cancer by personalizing medicine to advance cancer care beyond the standard chemo and radiation.
Dig Deeper:

We are here to support your cancer questions in an effort to help you make better, more informed decisions for your pet. It starts with a conversation. We are all ears!
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