Lymphoma

What is lymphoma?

Lymphoma, or lymphosarcoma, is the most common form of cancer in both humans and small animals. It is a malignant tumour that affects the lymph system, which makes up part of your dog’s immune system that protects against infection.

Lymphoma can occur anywhere there is lymph tissue such as in the lymph nodes, liver, spleen, gastrointestinal tract and skin. Most often, lymphoma originates in the lymph nodes before spreading to other organs in the body. There are several breeds known to have a higher incidence of lymphoma including Boxers, Bull Mastiffs, Basset Hounds, Saint Bernards, Scottish Terriers, Airedale Terriers and Bulldogs.

There are several different forms of lymphoma, which are classified by the area of the body they affect:

• Multicentric lymphoma: affects the peripheral (near the skin’s surface) lymph nodes. It is the most common form of lymphoma and accounts for about 80% of all canine lymphomas.
• Alimentary lymphoma: affects the gastrointestinal tract and accounts for about 10% of all canine lymphomas.
• Mediastinal lymphoma: affects the lymph tissues of the chest and is uncommon.
• Extranodal lymphoma: affects the skin, eyes and other areas. This is the rarest form of lymphoma.

Lymphoma typically affects middle-aged dogs. Most dogs show no signs of illness to the disease before diagnosis, making it difficult for vets to catch early. With this type of cancer, the goal is for a long remission rather than a cure.

Causes

As with many pet cancers, the direct cause of lymphoma is not known. With respect to this type of cancer however, possible contributing factors may include viral infection, direct contact with herbicides or pesticides, magnetic field exposure, genetic abnormalities and dysfunction of the immune system.

Symptoms

Many dogs with lymphoma show no distinctive signs of illness. Symptoms will vary depending on the form of lymphoma and how far the disease has progressed:

• Early signs of multicentric lymphoma include non-painful enlargement of the lymph nodes, which can be seen or felt as hard, rubbery lumps in various sites on the body such as under the jaw, in front of the shoulders or behind the knee. In later stages of this form of lymphoma, symptoms may include loss of appetite, lack of energy, weakness and/or fever.
• Symptoms of Alimentary lymphoma may include vomiting, abdominal pain, loss of appetite and continued weight loss.
• Signs of mediastinal lymphoma may include trouble breathing — as result of pressure on the lungs from fluid build-up in the chest — excessive thirst and urination.
• Symptoms of extranodal lymphoma will depend on which body part is affected such as the skin (sores that heal slowly or presence of widespread scaly sections); lungs (difficulty breathing); kidneys (kidney failure); or central nervous system (seizures).

Diagnosis

A thorough physical exam is a good first step in the diagnostic process to help determine what further tests, if any, are needed, and to rule out other causes of your dog’s illness besides lymphoma.

A full blood work-up and urinalysis will be part of the exam. These tests will help confirm whether or not your dog has lymphoma, whether or not chemotherapy drugs — the most effective treatment for lymphoma — can be safely administered and to help predict your dog’s response to treatment.

If lymphoma is suspected, the best way to confirm this diagnosis is to perform a biopsy — a minor surgical procedure that removes a piece of the lymph node or other organ suspected of being cancerous.

Once a definitive diagnosis of lymphoma is reached, your vet or specialist will want to determine the stage of lymphoma, which is the extent to which the cancer has spread throughout the body. The stage of lymphoma will determine the manner in which your dog will be treated.

Stages

Stage I: only one lymph node involved
Stage II: several lymph nodes in the same general area involved
Stage III: all peripheral lymph nodes involved
Stage IV: all peripheral lymph nodes plus the spleen, liver, and/or anterior mediastinum in the chest involved
Stage V: bone marrow involvement, regardless of any other areas involved

Substages of lymphoma

Substage a: without any signs of disease (the dog shows no symptoms)
Substage b: with signs of disease (the dog is not feeling well)

Knowing the substage (ie: Stage IIIa or Stage IIIb) is important for determining how fast a patient achieves remission and how long it lasts. Patients have a much better chance at a long remission if treated during substage a, when they are feeling well.

Treatment and Prognosis

Chemotherapy — the treatment of cancer with the use of a variety of drugs is the most effective treatment for most forms of lymphoma. The types of chemotherapy drugs used as well as the dosage, frequency and duration, are determined by the stage of the disease and other factors established during diagnostic testing. Fortunately, most dogs tolerate chemotherapy well so their quality of life during treatment is usually good.

With respect to treating lymphoma, the goal is to achieve a state of prolonged remission, either partial or complete. Partial remission means that the cancer has been reduced by at least 50 per cent and complete remission means the cancer is no longer present. If lymphoma is left untreated, most patients will die of the disease in four to six weeks from diagnosis.

Treating multicentric lymphoma, the most common form of lymphoma, with chemotherapy is very effective, with about 90 per cent of all dogs improving to some degree. Most multicentric lymphoma patients on chemotherapy will live for about a year while 25 per cent of these dogs will live for about two years. And about 60 to 90 per cent of these cases will result in complete remission.

Treating other forms of lymphoma is more difficult. Alimentary lymphoma, if concentrated in one area, can be treated effectively with a combination of surgery to remove the tumour and chemotherapy. However, if the lymphoma has spread throughout the intestinal tract, treatment is not as effective and the rate of survival is reduced significantly.

Mediastinal lymphoma can be treated with chemotherapy, with or without radiation therapy. This may significantly improve survival times and quality of life. Extranodal lymphoma can be managed with surgery, radiation and whole system chemotherapy depending on the area affected.

Unfortunately, most dogs with lymphoma will have a relapse at some point. For many of these dogs a second remission is possible but does not usually last as long as the first remission. Eventually most lymphomas become resistant to chemotherapy drugs and the dog succumbs to the disease or is euthanized.

Immunotherapy – is a form of cancer treatment that uses the power of the body’s own immune system to prevent, control, and eliminate cancer. There are several different immunotherapy approaches to cancer, in the case of Lymphoma, Monoclonal Antibody therapy in conjunction with chemotherapy has been shown to improve life expectancy. It is not suited for all types of Lymphoma so a detailed diagnosis of the type of Lymphoma is necessary.

Sources:

• VeterinaryPartner.com, a Veterinary Information Network (VIN) company, Lymphoma in dogs, by Wendy C. Brooks, DVM, DipABVP, educational director.
• VeterinaryPartner.com, a Veterinary Information Network (VIN) company, Lymphoma, by Wendy C. Brooks, DVM, DipABVP, educational director.
• The Merck Manual Pet Health Edition, Canine Malignant Lymphoma.
• College of Veterinary Medicine – Purdue University, Canine Lymphomas.
• The National Canine Cancer Foundation, Lymphoma.
• CanineLymphoma.com, Canine Lymphoma Monoclonal Antibody Therapy.

This page has been reviewed by our Panel of Experts for accuracy. Our Panel of Experts is comprised of practitioners with varying specialties and perspectives. As such, the views expressed here may not be shared by all members of our Panel.

The content on this website is for informational purposes only and is not intended to be a substitute for professional veterinary medical advice, diagnosis or treatment.