By Sarah Hoggan, from the September 2000 Newsletter

Many people have witnessed a friend or family member battle cancer and are familiar with the regimes of chemotherapy, radiation treatments, or surgery. However, when cancer is diagnosed in a pet, the course of action is suddenly unfamiliar and owners are often unsure of the next step to take. Is treatment available, or is euthanasia the only humane choice? The answer depends on the situation.

First, an owner may want to know what cancer is and how it's classified. Cancer is essentially uncontrolled cell division and growth. While cell division is a normal biological process, when cancer is involved the cell divisions become aberrant. Instead of producing nicely-organized cells that are all the same size and have the same function, cancer makes them 'different.' Some cells are huge and some are small. Some cells produce hormones while others continue to divide and only produce more abnormal cells. This uncontrolled cell growth makes a tumor and allows the cancer to spread.

Next, cancer is classified in two basic categories: sarcomas and carcinomas. Sarcomas are cancers derived from structural tissues, such as bone, muscle, or connective tissue. An example of a sarcoma is osteosarcoma: a tumor commonly found in the long bones of the legs and in the jawbone or mandible.

Carcinomas are cancers derived from non-structural tissues such as skin cells, blood, and glandular tissue. Squamous cell carcinoma is an example of a carcinoma found in skin.

The only way to definitively diagnose cancer is by looking at it microscopically. A tumor may look very suspicious superficially or on a radiograph, but without looking at the cells that make it up, there's no way to know for certain if it is cancer or not.

The two most common ways to collect cells for diagnosis are a fine needle aspirate or a biopsy. With a fine needle aspirate, a needle is inserted into the tumor and some of the cells are drawn up. The cells can then be examined microscopically for changes consistent with cancer.

Unfortunately, some tumors don't shed cells very easily so a fine needle aspirate won't work then. A biopsy becomes the next option. A biopsy is a procedure where a piece of the tumor is cut off and then examined microscopically. Generally a biopsy is a more invasive procedure and may require surgery.

from the October 2000 Newsletter

Once cancer has been identified through a biopsy or fine needle aspirate, it's further categorized with a grade and a stage. The grade of the cancer is based on how it looks microscopically. Grade is equivalent to virulence, or in lay terms, aggressiveness. A cancer that has very few abnormal cells would be a lower grade than a cancer that appears very aberrant. Generally, the higher the grade, the worse the prognosis because a high grade cancer is often a very aggressive cancer that will spread.

Stage refers to the spread of the cancer; has it infected other parts of the body, or is it contained to one site? This is important to know because it helps determine prognosis as well as treatment options.

Cancer spreads throughout the body through metastasis. This is a process where small "satellites" of cancer travel through the blood stream or lymph to infect other parts of the body. Common sites of metastasis are the lymph nodes, liver, spleen, and lungs because these are organs that either filter the blood or have a very high volume blood supply. A low stage cancer means it hasn't spread and therefore carries a better prognosis. A high stage cancer means it has spread and infected other organs with metastasis. Metastasis can be identified by medical imaging or exploratory surgery.

Imaging is looking at the internal structures without cutting through the skin. Examples of imaging are radiographs or X-rays, ultrasound, CT scans, and MRI. These are usually the first choice for looking for metastasis.

Exploratory surgery is the other method of looking for metastasis. It's better in some situations than imaging because you can sample tissues directly to see if the cancer has spread.

Once cancer has been identified and is graded and staged, treatment options can be explored. A cancer diagnosis in a pet is not a sentence of immediate euthanasia. There are three common treatment options for pets with cancer: surgery, radiation therapy, or chemotherapy.

Surgery is the treatment that's most likely to be curative. Surgery removes the cancer from the body and doesn't impact other organs. For example, if your pet is diagnosed with a cancer of the jaw, removing the affected portion of the bone before the cancer metastasizes is curative because the cancer is gone. Surgery is only curative if the cancer hasn't spread, or if the other affected areas can also be removed surgically. Obviously for something like cancer of the white blood cells, or leukemia, surgery won't work because that cancer can't be cut out.

from the November 2000 Newsletter

If a pet’s cancer is inoperable, radiation therapy is another treatment option. Radiation can work well on a focused area of cancer that either can’t be treated surgically, or was treated surgically and some of the cancer remains in the tissue. An example where radiation would work is in a tissue that had a tumor removed but the cancer had spread to the local lymph nodes. The radiation can be focused to target only that area and spare the rest of the tissues and organs.

Radiation works by harming rapidly dividing cells. When irradiated, cancer cells can’t divide and spread, so they die. Radiation is often less curative than surgery and some cancers simply don’t respond to radiation treatment. Melanomas are an example of a cancer that doesn’t die from radiation because it is made of pigment-containing cells whose job is to absorb the sun’s radiation.

Chemotherapy is the third treatment option. It’s best for cancers that involve multiple sites or sites that aren’t susceptible to surgery or radiation. In veterinary medicine, chemotherapy is not curative. Many people think of loved ones they have seen endure chemotherapy and the image of a horribly sick individual comes to mind. While the drugs used in veterinary chemotherapy are the same as human chemotherapy, the dosages are very different.

Chemotherapy works by killing rapidly dividing cells. That’s why humans lose their hair and become so nauseated because hair cells and the cells of the GI tract are constantly dividing. The dosages of the chemotherapy drugs humans get are designed to kill all the rapidly dividing cells.

People can understand that they will feel terrible, but their cancer will be gone, so it is worth the misery. Pets can’t understand anything beyond the present so the dose of chemotherapy drug they receive is small, and still kills rapidly dividing cells, but only kills some of them. This lower dose means the cancer isn’t killed, but the animal feels fine. Pets can be on chemotherapy and still have a very high quality of life because they don’t have the high dose side effects that humans get. Some dogs will lose some of their fur, such as poodles and old English sheepdogs because their fur is constantly growing, similar to human hair. This however, is not a devastating side effect to the dog. Again, it’s important to understand that in veterinary medicine, chemotherapy isn’t meant to be curative. It’s a measure to provide the animal more time with a higher quality of life.

Finally, if all treatment options are exhausted or deemed ineffective, euthanasia is a kindness available to veterinary patients. When everything that can be done has been done, and the animal is suffering, euthanasia can painlessly end the misery. The decision to euthanize is very difficult and very personal. Consulting your veterinarian who has treated your pet may help. They know your animal and like you, have their best interests in mind.

Sarah Hoggan is a senior veterinary student at WSU's College of Veterinary Medicine. Upon graduation she plans to become a small animal veterinarian.
Sarah and Steve Hoggan are at last parents! On September 10th Tucker Drummond Hoggan was born: 7 lbs. 11 ounces; 20.5 inches long. Everyone in the family is happy and healthy; including the pets!

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