Canine Lymphoma – Cancer in Dogs

Canine lymphoma, similar to non-Hodgkin’s lymphoma in humans, accounts for roughly 7 to 14 percent of all canine cancers and is one of the five most common for dogs. There are more than 30 described types and they can vary significantly in their behavior.

What is it?

A lymphoma arises from white blood cells called lymphocytes, which help the immune system fight off infections. Consequently, most lymphomas are found in organs that are part of that system.

While lymphoma can affect almost any of those organs, it’s most often seen in the lymph nodes under the jaw, in front of the shoulders or behind the stifle (knee) before spreading to another organ, such as the spleen, liver or bone marrow. Some lymphomas progress rapidly and require aggressive treatment, while others move very slowly and can be managed as a chronic disease. Like most canine cancers, lymphoma has no known cause.

The four most common types are multicentric (80 to 85 percent of lymphomas), affecting the lymph nodes; alimentary (7 percent of lymphomas), affecting the intestines; mediastinal, affecting the thymus and nodes in the chest; and extranodal, affecting a specific organ, such as the skin, eyes, kidneys, lungs or central nervous system. (If the bone marrow is involved, the diagnosis is lymphocytic leukemia.)

Signs and symptoms.

In lymphoma’s early stages, a dog owner may notice a lump under the jaw or in the dog’s neck without the dog showing any signs of illness. Some dogs may exhibit only mild tiredness or a reduced appetite, while others will have more serious symptoms, such as weight loss, weakness, GI problems, excessive thirst or difficulty breathing. Swollen, non-painful lymph nodes are a consistent sign.

Lymphomas that appear on the skin (cutaneous lymphomas) are sometimes first diagnosed as an infection or an allergy; they start with red, flaky, itchy patches that eventually become red, moist, open sores. Gastrointestinal lymphomas present with vomiting; dark, watery diarrhea; and weight loss. Lymphomas that appear in the chest can cause a dog to have difficulty breathing and/or to develop a swollen face and front legs.

How is it diagnosed?

To diagnose lymphoma, the vet will biopsy the affected tissue and follow up with a series of tests to determine how far it has developed. Blood and urine are evaluated, the chest and abdomen are X-rayed, and a sonogram of the abdomen and a bone marrow aspirate may be recommended. Abnormalities revealed by the sonogram are often sampled via fine needle aspirate, a well-tolerated way to obtain a specimen of the mass.

How is it treated?

Depending on the type, lymphoma is generally considered to be treatable, and chemotherapy is the preferred method.

According to experts at Colorado State University’s Flint Animal Cancer Center, “Canine lymphoma is initially very sensitive to chemotherapy. Up to 95 percent of dogs treated will go into remission when the most effective treatment protocols are used.” These protocols involve a combination of drugs given over several weeks to several months and is based on a similar protocol used for lymphomas arising in people.

A recent therapy, Tanovea-CA1, which has received conditional approval from the FDA, is very promising. It can be used alone or in combination with other drugs and involves five intravenous infusions of the drug at twenty-one-day intervals. The drug is expensive but can result in a lower overall cost, since the course of treatment tends to be shorter than other options.

Dogs treated for lymphoma tend to have a very good quality of life and often remain in remission for a year or more. Roughly 20 percent of dogs survive more than two years with appropriate treatment.

Are certain breeds predisposed?

Lymphoma can develop in any breed at any age, although Golden Retrievers seem to be the most commonly affected, followed by Boxers, Bullmastiffs, Basset Hounds, Saint Bernards, Scottish Terriers, Airedales and Bulldogs.