Questions About Pet Cancer?
VOSRC Can Help

Just as in human medicine, cancer in our veterinary patients is a complicated disease. Researchers do not fully understand how or why some animals get cancer while others do not. There are some known factors that could lead to prevention. In dogs, there are known breeds predisposed to certain types of cancer, thus suggesting a genetic component. Using pedigree analysis, we have recently reported inheritance of lymphoma and soft tissue sarcomas in golden retrievers. However, only about 5% of cancers overall in humans are genetic. Finding  cancer-causing genes in dogs is in the near future.

Certain cancer causing environmental factors or carcinogens are also known, including sun exposure, passive smoking, and exposure to pesticides, just to name a few. There are known effects of sex hormones in causation of cancer in dogs. Spaying female dogs at a young age prevents the development of mammary tumors. Male sex hormones influence the development of bone and prostate cancer in dogs. But in the end, the development of cancer in most cases results from a cascade of events.

Yes. Tumors may be benign or malignant, just as in people. Benign tumors usually do not spread, and while they may affect local tissues, they are not invasive or aggressive. In general, when people use the word cancer, they are referring to malignancies, which can spread by metastasizing to other parts of the body. Many times, these tumors grow very rapidly and can be very dangerous. In addition, different cancers can be more serious because of their behavioral tendencies or the specific organs or tissues they affect.

However, the more rapidly growing tumors are also potentially more sensitive to therapy, especially chemotherapy. Lymphomas are amongst the most aggressive cancers and yet have at least 80% complete remission induction rates with chemotherapy. Because of their rapid rate of disease progression, lymphoma cases in dogs and cats are scheduled for initial consultation within 24–48 hours of first contact with VOSRC.

There is currently no way to avoid all cancers. Just like in people, a quality diet and avoiding substances that have been deemed carcinogenic may have a positive impact. Anything that potentially could cause cancer in a human likely can cause cancer in our pets. For instance, animals also may get skin cancers related to sun exposure. Paying attention to these and other “common sense” things may help reduce the likelihood of your pet developing cancer.

It is estimated that 6 million of the 65 million dogs and 6 million of 32 million cats are diagnosed with cancer each year. Mortality rates from the various types of cancers have not been calculated as it has been in human oncology. It is known that cancer is the primary cause of death in pets over age 10. That statistic can be changed with effective treatment in the geriatric cancer patient, while maintaining the dignity that our long-standing family members deserve. At VOSRC, we do not use the numerical age of the pet to make recommendations to treat. We look at the overall well-being of the individual patient both medically and emotionally. A prime example of this is that Dr. Jeglum treated Rocky, her 22-year-old cat, for a nasal tumor with radiation therapy, and he died of old age a year and half later. Rocky’s physical condition and strength of spirit helped make the decision to treat.

We are strong advocates of the prophylactic use of anti-nausea drugs (anti-emetics) rather than allowing gastrointestinal side effects to develop and then initiating medications. There are now newer anti-emetics that are much more effective in preventing vomiting and diarrhea.

Myelosuppression (lowering of blood counts) secondary to chemotherapy is not life threatening with the use of prophylactic antibiotics and bone marrow stimulating factors when necessary. Lowered white blood cells (leukopenia) and red blood cells (anemia) can both be treated with stimulants. There are no stimulants for the blood clotting cells (platelets); therefore, thrombocytopenia (low platelets) has to be watched carefully with certain chemotherapy drugs. If a protocol is known to cause a drop in the infection-fighting white blood cells (the neutrophils), antibiotics may be prescribed at the time of administering chemotherapy.

Less than 5% of our patients ever require hospitalization relating to treatment toxicities. We tell all our owners that there may be a few bad days here or there but the good times will outweigh the bad! In many cases a reaction is not from the drugs themselves, but due to response to therapy. Tumor breakdown or killing of the cancer can cause the patient to feel ill—but that is a positive endpoint.

Radiation therapy is one of the modalities used to treat cancer in your pet. Ionizing radiation enters the body via a small controlled portal, or external beam, and works by damaging the DNA of the exposed tissue. Cells that are cancerous are susceptible to death due to faulty DNA that cannot repair itself like normal, healthy tissue. This normal tissue is spared due to the direction and shape of the radiation beams.

Radiation is effective in controlling tumor growth as a sole modality, but it also can be used in conjunction with other treatment modalities such as surgery and chemotherapy. If radiation is the appropriate therapy, your pet’s field can be determined by radiographs  or digital films, MRI, or CT scans.

During all procedures from simulation (initial set up) to the actual treatment, the animals are anesthetized with fast-acting anesthetics and monitored by a veterinary technician and veterinarian. Following the day of simulation, the actual treatment time is a matter of minutes, depending on the number of treatment fields. The type of machine that delivers the beam is called a linear accelerator. Accelerators produce x-rays, or photons, as well as electron beams. The higher energy photon beams are used for tumors that are located deeper in the tissue. Electron beams are usually used for more superficial types of tumor. Radiation works in the tissue by arresting and not allowing the tumor cells to reproduce and grow, resulting in shrinkage and, in many case, eradication of tumor.

There are typically two types of treatment plans for animals undergoing radiation: definitive and palliative. Definitive is therapy to be delivered when the animal is assumed to benefit from long-term control of the tumor. This type of treatment is typically done over the course of three to four weeks, usually five a week on Monday through Friday. Treating this way does sometimes cause acute side effects to the local area being treated. These are manifested as a radiation dermatitis, which manifests as skin irritation, reddening, itching, and hair loss. Side effects in most cases are temporary and transient and will vary depending on location and tumor type. Self-trauma (i.e., licking) must be avoided. Close supervision and daily monitoring of your pet is important. We like to hear your daily feedback.

Palliative therapy is given with the goal of relieving pain and improving quality of life. These patients are treated less frequently and at a lower total dose, typically once weekly for four to six weeks. This allows the patients who may not benefit from definitive therapy to spend more time at home with their family and to experience fewer side effects.

The good news is there are no systemic side effects since we are not irradiating internal organs, as is done in different types of human malignancies. In pets with head and neck tumors, feeding tubes can be utilized to improve nutritional status. However, they are not used with the frequency as in humans.  An owner does not need to fear radiation therapy as they often do; it is very different for our pets than it is for humans.