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Canine Lymphoma

Lymphosarcoma, also known as canine lymphoma, is the most common type of cancer in dogs, but has only recently been recognized and treated. The first case was documented in the late 1980's in a mutt-i-gree dog who subsequently died. The disease was universally fatal in less than a year in these early days, but advances in veterinary science have led to lymphoma now having a fairly high remission rate.

Lymphoma lumps can be found in the neck, abdomen, armpits or back.

Who gets lymphoma and how?

Although any breed of dog can contract lymphoma, some breeds are more likely than others to develop the disease. The breeds most likely to develop lymphosarcoma are Golden Retrievers, Basset Hounds, Beagles, Rottweilers, Poodles, Pit Bulls, Boxers, German Shepherds, and Scottish Terriers. Lymphoma most often strikes a dog during middle age.

No one knows exactly how lymphoma develops, but it is thought that there is a genetic link as well as an environmental one. It is likely that a genetic predisposition causes one or more cells to mutate into cancer cells, possibly in association with an infection or under the influence of environmental factors like chemicals, cigarette smoke and exposure to ultraviolet light. The method in which any one specific dog gets cancer does not determine that dog's treatment or prognosis, so it is not important that you try to locate the cause or place blame when your dog is diagnosed.

Where does lymphoma strike?

Lymphosarcoma attacks the lymph tissues of the dog, which is spread out in many areas throughout the body. The purpose of the lymphatic system is to filter fluids from the body's tissues to help fight off disease. Lymph vessels are found throughout the body, draining into lymph nodes and the other organs of the lymphatic system: the tonsils, spleen, bone marrow, and throughout the digestive system.

Multicentric lymphoma, the most common type, affects the lymph nodes located just under the skin along the jaw line and at the tops of the legs where they join the body. Gastrointestinal lymphoma attacks the digestive system and can prevent your dog from digesting food and absorbing nutrients. Mediastinal lymphoma occurs in the chest of the dog and can interfere with lung function. Extranodal lymphoma is the rarest type, starting in breast tissue, skin, the liver, eyes, bone tissue, or the mouth. Although these areas are outside the lymphatic system, the cancer often spreads to become multicentric lymphoma as the disease progresses.

How is lymphoma diagnosed?

The initial symptoms of lymphoma are variable, depending on where the disease starts. However, there are certain hallmark signs that are present in nearly all dogs who have lymphosarcoma.

Lumps are often the most obvious sign. They are usually round and hard, located in the abdomen, armpits, back, or neck. Your dog may begin to eat less than normal or even totally lose interest in food. The dog may also begin to cough or vomit after eating on a regular basis. This in turn leads to rapid weight loss, another key sign of illness. A dog who has a fever for longer than three days or one that reoccurs frequently may be having a problem with his or her immune function, of which the lymphatic system is a part.

If you notice these symptoms, particularly in combination, your vet will need to do some diagnostic tests to determine the cause. In addition to a physical exam to check the size and texture of the dog's lymph nodes, your vet will likely do a urinalysis and blood test to check the dog's overall health.

What does tumor stage mean?

A definitive diagnosis is only possible by taking a biopsy of one of the enlarged lymph nodes. Based on the biopsy, as well as other tests which can be done, your vet may attempt to stage the tumor to assess how far it has invaded your dog's system. Stage I means that only one lymph node is involved, while Stage II shows involvement in several lymph nodes, but only in one part of the body. Stage III involves all of the peripheral lymph nodes. Stage IV indicates that all peripheral lymph nodes plus the spleen, liver, or mediastinum. Stage V indicates involvement of the bone marrow, regardless of whether or not other nodes and organs are involved.

Staging indicates only the location of the disease, not necessarily the prognosis. Stages I through IV are generally responsive to chemotherapy, while Stage V generally is not. Within each of the stages are two subtypes: a and b. A dog who is feeling basically well at the time when diagnosis is made is staged with a subtype of a, and has a better chance of achieving a higher quality remission. Conversely, subtype b dogs exhibit symptoms such as vomiting or loss of appetite. They are likely to take longer to get into remission and stay in remission for a shorter period of time.

Chemo drugs may be administered by IV.

Treatment options for canine lymphoma

As the malignant cells grow and multiply, they crowd out the normal cells in the body's organs, causing these organs to fail. The goal of therapy is to reduce the tumor load, allowing the organs to function more closely to normal, allowing the highest quality of life for the longest period of time.

Without treatment, dogs will usually die from lymphoma within 2 months after diagnosis. It is vital that dogs be diagnosed as soon as you begin to notice symptoms so that treatment can be started in a timely fashion.

Chemotherapy is the most effective treatment for lymphoma, and may be used in combination with radiation treatment of localized tumors. The least desirable form of treatment for most lymphomas is surgical removal of the tumor. It is typically used only when the tumor is encroaching on vital organs, and only after the tumor has been treated with chemotherapy.

Just as in humans, chemotherapy involves injecting poisons into the dog's bloodstream to kill cancer cells. The problem is that chemotherapy drugs are targeted to attack rapidly growing cells, which includes not only tumor cells but some normal cells as well. Veterinary oncologists are constantly researching to find a combination of drugs that have the highest effectiveness against tumor cells and the lowest toxicity for normal cells.

The chosen combination of drugs, as well as when and how they are given, is called a protocol. In consultation with your vet and possibly with a veterinary oncologist, you can choose the protocol that is the best both for your dog and for you and your family. The drugs most commonly used include cyclophosphamide, vincristine, doxorubicin, and prednisone.

What are the side effects of canine lymphoma chemotherapy?

When chemotherapeutic drugs attack normal cells, they can cause side effects such as suppression of the bone marrow and a low white blood cell count, leading to an increased chance of infections. A drop in red blood cell count can result as blood cells are killed off, leading to anemia. When the drugs affect the dog's hair follicles, hair loss results, especially around the face, paws, and near the tumor.

Proper nutrition during chemotherapy is vital. While your dog is receiving chemotherapy, your vet may recommend that you give the dog nutrients which are known to boost the dog's immune system. Glyconutrients are often marketed as immune system boosters. In addition, dog foods high in protein may help starve cancer cells while those high in carbohydrates feed the tumor and allow it to grow faster. Omega-3 fatty acids have also been found to be effective against lymphoma.

How do I know which treatment to choose?

There are many factors to consider when choosing a treatment regimen for your dog. Sometimes because of financial factors or advanced disease, the most humane choice may be to put the dog down soon after receiving the diagnosis. In other cases, you may choose to go all out to achieve as many remissions as you can for as long as you can.

In reviewing the various protocols, you will want to ask several questions:

• How long do remissions usually last?
• How quickly are remissions achieved?
• How many remissions are typically seen?
• How long do most dogs last before ultimately succumbing to lymphoma?
• How expensive is the treatment?
• What type of schedule must be maintained – how often are treatments required?
• Can treatments be given at home or must the dog stay overnight at the clinic?

One of the most common treatment protocols was developed at the University of Wisconsin – Madison. The dog is given weekly treatments for 9 weeks, then receives 7 more treatments evenly spaced over the next 14 weeks. The animal is then re-checked monthly to catch recurrences as soon as possible.

As many as 80 – 90% of dogs achieve at least a first remission using this protocol, and the first remission generally lasts 10 – 14 months. When remission ends, chemotherapy is re-started and 70 – 80% of dogs go back into remission. With each cycle, the number of dogs achieving remission and the length of remission are decreased as the cancer cells become resistant to the protocol drugs.

About 20% of dogs make it past two years. Although this sounds like a short time, remember that your dog was likely already in middle age, and two years may be 50% or more of what his or her remaining life expectancy would have been without the disease.