Veterinary Oncology Falsehoods and Fallacies: Part 1

Kimberly Reeds, DVM, MS, DACVIM (oncology)

Cancer is scary. Hearing of a cancer diagnosis made in a friend or family member, even our furry family members, often results in fear and worry. Virtually all of us has had someone close to us go through cancer treatment, and while the cancers that arise and treatments that are used are often similar between pets and man, the overall cancer experience is usually quite different.

Many people aren’t aware that cancer specialists exist in veterinary medicine. The fact is that there are many specialties in veterinary medicine, just as there are in human medicine. An oncologist is a specialist that obtains advanced training in the diagnosis and treatment of cancer.

Today we are going to review some of the common misconceptions about cancer in pets, and why they are wrong.

Fallacy #1 – Pets don’t get cancer like humans do.

Truth: Unfortunately, cancer is the leading cause of death in elderly animals. Studies indicate that 50% of dogs and approximately 35% of cats in the United States will be affected by some sort of tumor in their lifetime. The cancers that arise in humans and pets are often similar. Some of the most common cancers to arise in people, such as bladder cancer, liver cancer, melanoma, lymphoma, and thyroid cancer (www.cancer.gov) are also common in our pets. Research that advances diagnosis and treatment in humans is often used to improve the management of the same cancer in our pets. However, there are some instances, such as melanoma, in which the technology developed to treat pets allows for the advancement of treatment for humans.

Fallacy #2 – Cancer isn’t treatable in pets.

Truth: Some people wonder why we treat pets with cancer. A simple answer is because we can! Cancer can be considered a chronic disease without a cure, similar to other chronic diseases such as diabetes, kidney failure, and heart disease. Sometimes cancer is curable, but even when it isn’t, we can often control the clinical signs of the disease thereby extending how long the pet lives while maintaining a high quality of life.

The treatments used for human cancers are often the same in pets. Surgery, chemotherapy, and radiation therapy are all available to treat pets with cancer. The type of cancer and how advanced it is allows us to determine which option, or combination of options, would be best for the pet.

Fallacy #3 – The presence of a tumor is the only sign in a pet with cancer.

Truth: While the presence of a mass or tumor is one of the most obvious signs that a pet may have cancer, there are often more subtle indications that a cancer (or some other disease) may be present. These include:

A non-healing wound or sore
Decreased appetite
Weight loss
Difficulty chewing or swallowing
Bleeding from a body cavity
Offensive odor
Loss of stamina or reluctance to exercise
Persistent lameness or pain
Difficulty with normal bodily functions such as breathing, urinating, or defecating
Swelling of the abdomen

If you see any of these signs, they should be investigated by your primary care veterinarian. Early detection and diagnosis often increases the chance of a successful treatment outcome.

Fallacy #4 – The technologies to diagnose and workup people with cancer aren’t available for pets.

Truth: Many of the same technologies are used to diagnose both the primary tumor and any area of spread (metastasis) in pets and humans. The workup for a pet suspected to have cancer may start with blood work. A complete blood count (CBC) and chemistry profile are usually recommended. While few animal cancers are detectable in the blood (this is different than in humans), the results of these tests may indicate problems with the internal organs that need to be investigated further. Decreased organ function may affect how the patient metabolizes and clears drugs from the body.

If the internal organs aren’t functioning properly, certain drugs cannot be used or if they are used, they need to be prescribed at a lower dose. Changes in the blood work results may also indicate that the cancer has spread to the internal organs, which would decrease the patient’s prognosis and overall life expectancy.

If a mass is present, sampling of the mass is vital. In veterinary medicine, one of the quickest and easiest ways to diagnose a tumor is with a fine needle aspirate (also called a needle biopsy). This technique samples the tumor (or other area of interest) to obtain cells to put on a slide. The slide is then sent to the lab where a veterinary specialist, the clinical pathologist, will examine the slide to determine what cells are present. This is called cytology. If the cells are in a high enough number, and have enough criteria to identify what cell type they are, a diagnosis of the tumor is made. For some cases of cancer, this diagnosis is enough to proceed with either further testing to determine how far the tumor has spread, or proceed with treatment. However, there are some cancers that further information is needed. This can occur when an inadequate or non-representative sample is obtained or when the cells cannot be identified. In these situations, a biopsy is often recommended.

There are many different ways to take a biopsy, but the main goal is to obtain a piece of tissue. This piece of tissue is then sent to the lab for processing and evaluation by another veterinary specialist, the anatomic pathologist (see, we have already identified three different kinds of veterinary specialists!). The pathologist examines not only the cells that are present, but how the cells are arranged in the surrounding tissue. If the cells still cannot be identified, further testing called immunohistochemistry (using special stains to identify the cells) or even DNA testing can be used.

Once the tumor is diagnosed, we must then determine how far the cancer is spread. Diagnostics such as x-rays or ultrasound are often used to examine the internal organs to determine if there is evidence of metastasis. CT scans and MRIs are recommended for some cases, and there are even facilities that are able to do PET scans (this isn’t a scan of a pet, rather it is a specialized way to look at the body in its entirety to identify areas of concern).

Once we know what the cancer is and how far it has spread, we are then able to discuss the most appropriate treatment plan for the pet. There are also many fallacies regarding cancer treatment in pets, which we will review with our post in 2 weeks. As for next week, come back to hear Dr. Holland discuss a very interesting case that we recently had in the hospital!