The Pet Tree House - Where Pets Are Family Too : Lymphoma in Dogs

Sunday, August 17, 2014

Lymphoma in Dogs

Canine lymphomas are a diverse group of cancers, and are among the most common cancers diagnosed in dogs. They collectively represent approximately 7-14% of all cancers diagnosed in dogs. There are over 30 described types of canine lymphoma, and these cancers vary tremendously in their behavior. Some progress rapidly and are acutely life-threatening without treatment, while others progress very slowly and are managed as chronic, indolent diseases. Lymphomas may affect any organ in the body, but most commonly originate in lymph nodes, before spreading to other organs such as the spleen, liver, and bone marrow.

What is lymphoma?
The term “lymphoma” describes a diverse group of cancers in dogs that are derived from white blood cells called lymphocytes. Lymphocytes normally function as part of the immune system to protect the body from infection. Although lymphoma can affect virtually any organ in the body, it most commonly arises in organs that function as part of the immune system such as the lymph nodes, spleen, and bone marrow. By far the most common type of lymphoma in the dog is multicentric lymphoma, in which the cancer first becomes apparent in lymph nodes.

Other common lymphomas in dogs include cutaneous lymphoma (lymphoma of the skin), alimentary or gastrointestinal lymphoma (lymphoma of the stomach and/or intestines) and mediastinal lymphoma (lymphoma involving organs within the chest, such as lymph nodes or the thymus gland).

What causes lymphoma in dogs?
Unfortunately, the cause of lymphoma in dogs is not known. Although several possible causes such as viruses, bacteria, chemical exposure, and physical factors such as strong magnetic fields have been investigated, the cause of this cancer remains obscure. Suppression of the immune system is a known risk factor for the development of lymphoma in humans. Evidence for this includes increased rates of lymphoma in humans infected with the HIV virus or are on immune-suppressing drugs following organ transplantation surgery. However, the link between immune suppression and lymphoma in dogs is not clearly established.

How is canine lymphoma diagnosed?
The best way to diagnose lymphoma is to perform a biopsy. A biopsy is a minor surgical procedure to remove a piece of lymph node or other organ affected by cancer. The most common methods for lymph node biopsy are Tru-cut needle biopsy, incisional wedge biopsy, or removal of an entire lymph node (excisional biopsy). The larger the biopsy sample, the better the chance for an accurate diagnosis of lymphoma.

We routine perform biopsy procedures to diagnose canine lymphoma at the Purdue University Veterinary Teaching Hospital (PUVTH). Dogs are placed under heavy sedation or general anesthesia to perform a biopsy. Although discomfort associated with this procedure is typically minimal, we often prescribe oral pain medication afterwards just to be sure your dog is comfortable following the biopsy.

How is canine lymphoma treated?
The most effective therapy for most types of canine lymphoma is chemotherapy. In some cases, surgery or radiation therapy may also be recommended. There are numerous chemotherapy treatment protocols for dogs with multicentric lymphoma. As discussed below, most dogs with lymphoma experience remission of their cancer following treatment, and side effects are usually not severe. Currently, the protocols that achieve the highest rates of remission and longest overall survival times involve combinations of drugs given over several weeks to months. The protocol we use as a “gold standard” for the treatment of canine multicentric lymphoma is a 25-week protocol called UW-25. It is based on a protocol called CHOP that is commonly used to treat lymphoma in humans.

The UW-25 protocol may not be appropriate for all dogs with lymphoma. Different types of lymphoma may be treated with different chemotherapy drugs. For instance, the most effective drug for cutaneous lymphoma is thought to be lomustine (CCNU). The veterinary oncologists and oncology residents at the PUVTH will help you decide on a chemotherapy treatment protocol that is appropriate for your dog.

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