Canine Lymphoma (Lymphosarcoma)
Canine lymphoma or lymphosarcoma is a cancer of the white blood cells and is a common cancer in dogs. We almost always consider lymphoma in dogs and cats to be a systemic disease—or a body-wide cancer—because white blood cells are part of the immune system; although, we may find evidence of this form of cancer only in the lymph node(s). Most commonly in dogs, the disease manifests in the lymph nodes and other lymphatic organs, such as the liver and spleen. Other sites of involvement include the gastrointestinal tract, kidneys, skin and central nervous system. Systemic treatment with chemotherapy is the preferred method to combat the disease. Rarely, treatments such as radiation therapy and surgery are used in the treatment of canine lymphoma.
Causes of Canine Lymphoma
Not much is known about the cause of lymphoma in dogs. Like all cancers, the development of lymphoma involves a mixture of genetic influences and environmental influences. Genetic information partially control how well an individual animal's system can correct damage to cells and to DNA, which can lead to cancer. Due to genetic factors, certain breeds of dogs, such as Golden Retrievers, are more likely than others to get lymphoma. Environmental influences often cause the damage that over time will lead to development of cancer. As pets and people age, they become less able to correct environmental damage to cells. The only known environmental influences linked to lymphoma in dogs are a banned lawn care chemical and possibly smoking in the household. There is most likely nothing you could have done to prevent development of cancer in your dog. In fact, your good care of your pet enabled him or her to live long enough to be able to develop cancer.
Stages of Canine Lymphoma?
- Stage I: one lymph node affected
- Stage II: two lymph nodes (on the same side of the diaphragm) affected
- Stage III: multiple lymph nodes affected
- Stage IV: the liver and spleen are affected
- Stage V: the bone marrow is affected (lymphoma and leukemia)
Stage I and II are very rare in dogs. Stage III is the most common presentation. Stage IV and V dogs will be a little less likely to go into remission with treatment than Stage III dogs. However, the most consistent predictor of whether a dog will go into remission or not is whether a pet feels well or sick when he or she is diagnosed with lymphoma. Dogs that feel well when first diagnosed tend to do the best.
Treatment Options and Potential Side Effects of Canine Lymphoma
We treat dogs with lymphoma using multi-agent chemotherapy (multiple different drugs). The goal of chemotherapy treatment for dogs is very different than the goal in treating humans. When humans are treated, the goal usually is to cure the cancer, and human patients may become very ill while on chemotherapy, although new drugs are being developed to deal with the side effects. When we treat pets, we want to put the disease into remission and to prolong life, but we also want to make sure that dogs feel well while they are being treated. Therefore, we use less chemotherapy pound for pound than they do in human medicine. Our main goal is to prolong a good quality of life for your pet.
Without treatment for lymphoma, most dogs will die within 4-6 weeks. We do not cure lymphoma when we treat, but with multi-agent chemotherapy, the majority of dogs will go into remission. For dogs in Stage III, 80-90% will go into remission. For those in Stage IV it may be 60-80% and for dogs in Stage V, about 50%. If a dog does go into remission, then a first remission of 9-14 months is most common. Second remissions can be obtained, but they are harder to obtain and do not last as long as the first.
The most common chemotherapy protocol is called a modified Wisconsin protocol and necessitates multiple visits over the course of 5 months. Most dogs feel well while they are on the protocol, as long as they go into remission. Side effects of the chemotherapy can occur, although they are not common. If side effects occur, the most common are gastrointestinal in nature, such as vomiting, lack of appetite, or diarrhea. Most dogs do not have side effects, and those that do often have only mild side effects, which are treatable with medication at home.
The second most common adverse effect of chemotherapy is a low white blood cell count, which is why a complete blood count is performed at specified times. A low white blood cell count can make a patient more susceptible to infection. Rarely, either the gastrointestinal signs or the low white blood cell count can be so severe that a dog becomes very ill and needs to be hospitalized. Very rarely, such adverse effects may be fatal. Most dogs will not lose their fur while on chemotherapy, although poodles and old English Shepherds may.
It is important to remember that we do not expect dogs to become sick on chemotherapy. If your dog is sick after a chemotherapy session, you will want to call and speak to a doctor here.
In summary, lymphoma is not cured in dogs, but we usually can obtain a significant increase in lifespan, and dogs usually feel well while being treated.