I figured now would be a good time to start discussing some of the cancers we see in dogs and cats. Let’s start with the most common cancer we see in both dogs and cats, lymphoma. We are going to limit this blog to lymphoma in dogs.
Lymphoma, or lymphosarcoma, is a cancer of lymphocytes, which are one of the white blood cells. The normal function of lymphocytes is to protect the body from infection and disease.
This cancer usually starts in the lymphatic system in the lymph nodes or glands, but can affect any area of the body including the spleen, liver, or bone marrow and in some cases, even the eyes, skin, or other organs. Lymphoma occurs when the normal lymphocytes become mutated and obtain the ability to divide faster or live longer than what they should. Lymphoma can occur in any breed, at any age, but typically dogs are middle aged to older when diagnosed. Breeds that are believed to be most at risk include Boxers, basset hounds, St. Bernards, and Scottish terriers.
The most common indication that your dog may have lymphoma is enlarged lymph nodes. The paired lymph nodes that can be palpated on the outside of the body are represented in the picture below.
If you feel lumps in these areas, you should have your dog examined by your primary care veterinarian. Other signs of lymphoma may include weight loss, vomiting, skin lesions, an abnormal appearance of the eyes, and enlargement of the abdomen.
The diagnosis of lymphoma is often straight forward. There are two main causes for multiple enlarged lymph nodes in a dog: a systemic cancer such as lymphoma or a systemic infection. Here in Oklahoma, tick borne diseases, such as Ehrlichia, are the most common infections to cause these changes, while in other areas of the country, certain fungal infections may be more likely. Typically, an aspirate or biopsy sample obtained from the enlarged lymph nodes will allow the veterinarian to quickly determine if it is either a cancer or an infection causing the enlargement. These samples will often need to be sent to a lab for confirmation of the diagnosis.
Once a diagnosis is confirmed, staging diagnostics can be performed to determine the extent of cancer involvement. The recommended diagnostics may include x-rays, ultrasound (sonogram), a CT scan, blood work, and bone marrow sampling. The results of these tests allow the disease to be put into a stage category.
Further classification of the lymphoma involves determining if the cancer is of T-cells or B-cells, which are the two main types of lymphocytes. This classification is important as it will allow a better understanding of the dog’s overall prognosis, and it may change what drugs are used to best treat the cancer. Dogs with B-cell lymphoma, the more common of the two types, will generally have a longer life expectancy and better response to therapy than dogs with T-cell lymphoma.
Chemotherapy is the treatment of choice for dogs with lymphoma. The chemotherapy options that are offered will include a multiple drug protocol, a single drug protocol, or steroids alone without chemotherapy. Multiple drug protocols, or combination chemotherapy, can result in response rates of greater than 90%, with an average life expectancy of one year. Approximately 20% of the dogs that live a year will go on to live two years or longer. Additional treatments that are available and may be recommended for your dog include a bone marrow transplant, radiation therapy, or Tanovea™-CA1, a new chemotherapy option that was recently released.
Overall, lymphoma is one of the most treatable cancers in dogs. It is well known that dogs that receive treatment experience an improved quality of life, for a much longer time, than dogs that do not receive any treatment. Most pet owners are pleased with the outcome and response to therapy that most patients experience. If you have additional questions or concerns about the use of chemotherapy in dogs or cats, please visit an earlier blog entitled Veterinary Oncology Falsehoods and Fallacies: Part II.