Oncology and Treating Cancer for Pets

Cancer is one of the leading causes of death in people. Over the last 20 years, it has also become one of the most significant health problems diagnosed in companion animals. People refer to cancer as if it was a single disease. In fact, there are many different forms and types of cancers that afflict both people and animals.

Cancers are classified based on several different criteria. One of the most significant classifications is based on the ability of the tumor to spread from a primary site to distant sites within the body. This allows the determination of malignant or benign to be assigned. Generally malignant cancers are highly aggressive and have the potential to spread within the body. Cancers that do not spread to other sites are classified as benign. Benign tumors may still be highly invasive into the tissues surrounding the mass. Malignant cancers may be further subdivided according to the original tissue type that they came from. Two large categories exist. Those categories are carcinomas and sarcomas.

It is not uncommon for dogs and cats to be referred for evaluation or treatment of cancer. It must be remembered that cancer represents a wide spectrum of diseases. Each tumor has different behavioral characteristics, rates of spreading, aggressiveness, cytokine or chemical production and growth rate. Because of these differences, the treatment of cancer is a very variable and complex undertaking. Although there are several methods that have been used to treat cancer, the most commonly used methods are chemotherapy, surgery, radiation therapy, immunotherapy or a combination. It is important to recognize that many tumors have very specific approaches and that inappropriate treatments may make the case worse.

Many solid tumors, especially benign ones, may be best dealt with surgery as a primary modality. The edges or margins of the mass are highly critical in whether or not the surgery was able to remove the entire mass. Regrettably, even if the margins are “clean”, there may still be microscopic spread or filamentous extensions, like roots from a tree that could be within the surrounding tissues. These remnants lead to recurrence of the mass. Surgery is often coupled with either chemotherapy or radiation therapy. These therapies are aimed at killing the remnant cells left after surgery.

Traditional chemotherapy involves the administration of drugs that inhibit cancer replication and energy systems. Once a medication is administered, the cancer cells will absorb it leading to cell damage and cell death. Unfortunately, non-cancerous cells are also affected by these medications. Usually, the normal tissues are able to repair the damage caused by the chemotherapy and resume normal function. When administered appropriately, chemotherapy does not elicit the severe adverse effects as seen in people. People will lose their hair, develop nausea and vomiting, muscle pain, joint and bone pain, general malaise and overall suffer unfavorable side effects. It is uncommon for these side effects to occur in dogs or cats. Naturally, the drugs do have side effects, but they are usually fairly minimal and do not significantly alter the pets quality of life. In actuality, most chemotherapy patients have had excellent quality of life during active chemotherapy.

Radiation therapy works by bombarding the cancer cells with ionizing radiation. In essence, the radiation induces mutations in the DNA (genetic code) of the tumor cells. This leads to an inability to manufacture various essential components and carry out cell functions. Eventually the cell may die. Radiation is commonly used after surgery for solid tumors. All Pets does not perform this treatment.

An exciting area of treatment involves immunotherapy. Several new drugs have been recently developed. Within this category are the vaccines therapies. These are currently available for melanoma and lymphoma, Palladia and Kinavet were originally approved for mast cell tumors in dogs, but have tremendous alternate uses in many other tumors. Metronomic chemotherapy uses very small amounts of conventional medications to impact tumor growth.

One important feature of cancer treatment is that there are often many different means to treat different tumors. Unfortunately, there is a variation in how people will treat certain tumors based on their experience, level of training, economic considerations of the owner, availability and ease in using methods, and characteristics of the tumor itself.

Common tumors we treat are lymphoma, hemangiosarcoma, mammary gland tumors, melanoma, mast cell tumors, osteosarcoma, thyroid carcinomas, transitional cell carcinoma and soft tissue sarcomas.

People will often ask me about remission times and such. Let’s first define “remission”. Remission is the absence of clinically detectable disease. What this means is that signs of the cancer are not detectable. You will note it does not say that the cancer is cured, just not detectable. Remission times are usually measured in months when dealing with cancer in dogs and cats. It is important to recognize that dogs and cats have significantly shorter lifespans. We tend to think of remission times as they apply to people. People typically live 70 or more years. A remission of 6, 9 or 12 months does not seem like a long time. In a dog or cat that may live 10-12 years, 9 months becomes a significant portion of their lifespan.

The decision to treat a pet with cancer is a very personal one. Many people have had a family member undergo cancer therapy and have many issues with putting their pet through similar treatments. Typically pets do not experience the same effects as people. This makes the disease worse than the treatment. Almost all chemotherapy medications are designed for people. Some may be very expensive. Owners must have realistic expectations regarding remission times and the commitment involved in treating a pet with cancer. Many of the treatment protocols require weekly visits for administration and follow up blood testing. There is always the potential for toxicity reactions.