The diagnosis of cancer often carries a wave of emotions. It is normal to feel overwhelmed and confused, however it is important to note that some types of cancers in pets are curable. For those cancers with no cure, there are many options to consider for treatment. The first step is to understand the diagnosis as well as the different treatment options in order to formulate a plan that best suits you and your pet.

Normal cells that make up your pet’s body grow, divide and die under strict regulations. What makes a cancer cell different from a normal cell is its ability to replicate uncontrollably, and invade (grow into) other tissues. A group of unregulated cells that forms a mass is often called a tumor, but not all tumors are cancer. Benign tumors can grow very large and press on healthy organs and tissues, but generally do not invade or spread to other parts of the body (metastasize). On the other hand, malignant tumors generally invade the surrounding tissues and spread to other areas in the body. When a cancer metastasizes, it spreads throughout the body through the lymphatic system or the blood stream.

Cancer in general is not the result of a single risk factor. Instead, cancer is the consequence of numerous mutations to the cells’ genetics that regulate cell growth and survival. Mutations can arise from genetic influences, exposure to environmental mutagens (cigarette smoke, ultraviolet irradiation, etc.), or other risk factors. As cancer research is advancing in veterinary medicine, we are able to identify more risk factors associated with the development of cancer.

No matter where a cancer may spread in the body, it is always named for the type of tissue where it originated. The three main categories include:
Epithelial Tissue - Epithelial tissue forms barriers in the body. Examples include the skin, linings of the respiratory, gastrointestinal, and urogenital tracts, as well as linings in glands and other organs. Malignant tumors that arise from epithelial tissues are considered carcinomas.
Connective Tissues - Connective tissues in the body include bone, muscle, tendon and blood vessels. Malignant tumors that arise from connective tissues are called sarcomas.
Discrete Round Cells - This set of tumors is grouped together based on their appearance under a microscope. Many are components of the blood or immune system. They include lymphocytes, plasma cells, mast cells, histocytes, and melanocytes. Malignant tumors are individually named based on subtype.

In certain types of cancer, grading the degree of malignancy is predictive of the clinical behavior. Tumor grade is based on distinct characteristics of the specific tumor when tissue is evaluated under the microscope (histopathology). In general, the tumor grade can help guide which treatment options are recommended.

Staging refers to the presence of disease elsewhere in the body other than the primary tumor. When we stage an animal, we generally request further diagnostics such as imaging (radiographs or X-rays, ultrasound, CT, MRI, etc.), lab work and/or fine needle aspirates. Staging allows us to see if the primary tumor has metastasized (spread) to other areas in the body. This allows the clinical team to assess your pet’s tumor burden, and make appropriate treatment recommendations.

Chemotherapy FAQ’s

Chemotherapy consists of a drug or combination of drugs given in order to kill rapidly dividing cells, such as cancer cells. Each treatment will kill a proportion of the tumor cells present. A number of treatments, or cycles, are given at regular intervals to reduce or eradicate the presence of cancer cells. Most pets receive 4-6 cycles of chemotherapy over the course of treatment. However, more chemotherapy may be needed to treat certain cancers. Chemotherapy drugs are commonly given intravenously (IV) during a hospital visit and your pet will go home the same day.

In people, complete remission is the goal of chemotherapy and this is best achieved by administering maximum doses over the shortest possible time frame. Toxicities that arise with this approach are managed by specialists in intensive care facilities. In veterinary oncology, chemotherapy is less aggressive and intense. It is aimed at gaining the best possible control of the cancer while avoiding the toxic effects. The goal is to give you the most time possible with your pet while maintaining his/her quality of life. The drugs administered in pets are similar or the same as those used in humans, but the doses are generally 2-3 times lower.

Chemotherapy targets rapidly dividing cells, such as tumor cells. Unfortunately, other rapidly dividing cells in the body are also affected by these treatments. These include the gastrointestinal tract (stomach, intestines, colon, etc.) and the bone marrow. The bone marrow serves a very important role in the body as it is the source of new blood cells.

Gastrointestinal Upset:

  • Decreased Appetite/Nausea/Vomiting
    • Most likely to occur 1-2 days after a treatment
    • Anti-nausea medications are given in hospital and sent home
  • Diarrhea/soft stools
    • In the week following treatment
    • Feed a bland diet (low-fat cottage cheese, white rice, lean boiled chicken, etc.)
    • Medications can be prescribed if soft stool persists
  • No pet should be expected to feel sick after chemotherapy. Please contact a veterinarian if you note these side effects in your pet.

Bone Marrow Suppression:

  • The bone marrow is the site of production for red and white blood cells and platelets. Neutrophils are white blood cells that are key players in preventing infection. They have a high turnover rate, thus are constantly being produced and destroyed. This makes them a target for chemotherapy drugs, which cause a predictable dip in cell counts at specific times after a treatment (between 3-14 days). This is why we check a CBC (complete blood count) when the neutrophil count is expected to be lowest. If the chemo causes these cells to fall below acceptable levels we will wait until they rise before resuming treatment with chemotherapy. These cell counts generally bounce back within 1-3 days. Your veterinarian may also provide antibiotics at this time to prevent infection while the cells regenerate and increase in number.
  • What to Look For:
    • Trembling, may be a sign that your pet has a fever due to infection.
    • Vomiting and diarrhea are also common signs of infection.
    • Call your veterinarian if you see any of these signs.

Take care in cleaning up after your pet if they have an accident in the house. Eliminations such as vomit, urine or feces, may contain residual chemicals for up to 4 days after treatment. Try to keep bodily fluids from coming into contact with your skin, eyes, or mouth, and wear gloves and wash your hands well after cleaning up.

Absolutely! However, take care to avoid exposure to bodily fluids (urine, feces, etc.) especially during the first week after a treatment cycle.

Hair loss is rare in animals to the extent that it occurs in humans. The fur may become thinner but does not result in overt baldness. Some breeds will be more affected than others (i.e. dogs that don’t shed regularly). Areas that have been shaved close to the skin may be slower to regrow, but your pets hair growth should resume once chemotherapy is over. Sometimes owners notice that re-growth occurs with a different color or texture than prior to treatment.

We recommend that your pet does not receive vaccinations while undergoing a chemotherapy protocol. Recent research indicates giving vaccines to a dog undergoing chemotherapy is safe, but the response to the vaccine may not be optimal. We generally recommend waiting 2 months after chemo to resume a vaccination schedule. We also ask that you have any homeopathic/herbal supplements discussed prior to starting chemotherapy, as many can have deleterious results when used in combination. You can continue giving flea and heartworm preventatives while on chemotherapy.