Kansas State University
Oncology Service
General Information for Owners

What does a diagnosis of cancer mean for my pet?
There are many different types of cancer that can occur in dogs and cats. It is very difficult to tell if a lump or abnormal growth is malignant based on appearance alone.

Two very important questions to answer when an animal is found to have a growth are:

1. What type of tumor is it?
   The actual type of tumor (for example: lymphoma, mast cell tumor, osteosarcoma) is very important in helping us to decide what the best treatment option will be. Some tumor types do not spread throughout the body (metastasize), and can be treated with surgery alone. Other tumor types are more aggressive, meaning that they will spread to other organs, such as the lymph nodes and lungs. The best way to know what type of tumor your pet has is by performing a biopsy. The biopsy will tell us if the tumor is malignant (likely to spread to other parts of the body) or benign (grows only in one area of the body), and this will also help us to know your pet’s long term outlook.

2. If it is malignant, how far has it spread?
   The answer to this second question is also very important in helping us decide the best treatment for your pet, and it may also help us estimate the long-term outlook. We will evaluate your pet for metastases by performing routine, non-invasive procedures such as x-rays and ultrasound. Some tumor types will spread to the bone marrow; in these situations a bone marrow aspirate will be recommended.

What treatment options are available for pets with cancer?
There are 3 basic treatment options for pets with cancer. These treatments may be used alone, or in combination, depending on the type of cancer diagnosed.

1. Surgery
   Surgery is used as the single method of treatment if the tumor is benign, or if the tumor is known to be very slow to metastasize. Surgery is combined with chemotherapy when the tumor is known to metastasize very quickly. Even if a search for evidence of spread has not shown any abnormalities, chemotherapy may be recommended if the tumor is known to be very aggressive. Surgery is combined with radiation therapy if complete removal of the tumor is not possible. In this situation, surgery is performed first and the surgery site is allowed to heal for 14 - 21 days before starting radiation therapy.

2. Chemotherapy
   Chemotherapy is very commonly used in dogs and cats with cancer. Chemotherapy drugs are used when the tumor has spread beyond the original site of growth, or when the tumor affects more than one area of the body. There are 2 equally important goals to keep in mind when using chemotherapy in the small animal cancer patient:

   1. Control the tumor for as long as possible, ideally cure the patient.

   2. Maintain a good to excellent quality of life for the patient throughout the duration of treatment.

   The chemotherapy drugs that are used for dogs and cats are the same drugs used in people. Because maintaining a normal quality of life is one of our main goals, we use chemotherapy somewhat less aggressively than in human medicine. Also, dogs and cats seem to be more tolerant of chemotherapy than people, and they do not suffer from as severe side effects.

   However, because chemotherapy drugs affect rapidly dividing cells, there are side effects that can occur in dogs and cats. There are 2 important sets of cells in the body that naturally grow and divide rapidly. These are the cells that line the bone marrow (which is where blood cells come from) and the cells that line the gastrointestinal tract. The types of side effects we see in our veterinary patients relate to these cells. We will monitor the blood count immediately before and 7 – 10 days after your pet has chemotherapy. If the blood count is low, chemotherapy will be delayed and the blood count will come back up on its own.

   At home, you may notice that your pet has a decreased appetite for 2 - 3 days after chemotherapy. You may also notice that they have softer stool than normal 4 – 7 days after chemotherapy. If your pet begins to vomit, or if the diarrhea is severe, DO NOT HESITATE TO CONTACT THE KSU-VMTH OR YOUR VETERINARIAN. There are medications that may be used to help minimize or control these side effects.

3. Radiation therapy
   Radiation therapy is also used frequently to treat dogs and cats. The most common form of radiation therapy is also called ‘external beam radiation therapy’. Typically, it involves multiple treatments over a course of 3 – 4 weeks. Animals must be under general anesthesia for each treatment. Radiation therapy is recommended for tumor types that are unlikely to spread beyond the original site of growth. Radiation therapy is typically used after surgery if the surgeons were unable to remove the entire tumor.

How do I decide whether or not to treat my pet’s cancer?
The diagnosis of cancer in a pet can be frightening and it brings up many difficult and sometimes confusing issues. Several treatment options may be offered, with one being the ‘best’ or most aggressive way to treat the disease and others being less toxic or financially more realistic. We would like to help you in any way possible with the decisions you face and would like to make sure you understand all the options offered.