Lymphoma is a type of cancer that arises from lymphatic tissue. In humans and in pets, the lymph nodes are frequent sites of these cancers. Lymphatic tissue is also found in bone marrow, the thymus (a small gland within the chest), the liver, the spleen, and in other places including the gastrointestinal tract and skin. In dogs, lymphoma may arise in any of these organs or tissues. Lymphocytes—a type of white blood cells—are the original source of these malignant lymphomas.
Also called lymphosarcoma (LSA), canine lymphoma involves the excessive growth of malignant cells in lymphatic tissue. Most commonly, domestic dogs are afflicted with a form of the disease called malignant multi-centric lymphoma by which it affects multiple lymph nodes throughout the body. It is a rapidly progressive disease that may also involve additional organs. Localized forms of lymphoma may also occur, but these are less common in dogs.
Possible Causes & Prevention
Evidence suggests exposure to certain toxins may be related to the risk of developing lymphoma. Dogs living in places where they may be frequently exposed to solvents, paints, pesticides, herbicides, smoke, and/or other toxins, appear to be more likely to be diagnosed with this form of cancer. Even excessive exposure to electromagnetic radiation—such as living near overhead power lines—may be linked to increased risk.
It’s unclear whether specific household chemicals are to blame for lymphoma. Common herbicides containing 2, 4-dichlorophenoxyacetic acid (2,4-D) have been implicated, but the link is controversial. Nevertheless, 2,4-D herbicides are known to be absorbed through the skin and into dogs’ bloodstreams if pets are allowed to walk on lawns soon after spraying. Lymphoma, like other forms of cancer, is a genetic disease. Although cancer is not “inherited”, certain hereditary genes that play a role in cancer development may be involved in dogs with lymphoma. Various breeds are more likely to get the disease.
Signs and Symptoms
Some dogs show no obvious signs of illness. Others may have noticeably swollen lymph nodes, in areas such as the underside of the neck and in the groin. Often, the enlarged lymph nodes are not painful. Other signs are less specific, and may include lethargy, coughing, diarrhea, vomiting, weight loss and listlessness.
Although symptoms tend to be nonspecific and may mimic the effects of infections or other diseases, a diagnosis of lymphoma is usually easily obtained with a needle biopsy. This is a relatively simple procedure that involves using a needle to remove a sample of cells from the affected area(s) for evaluation under a microscope. After obtaining a diagnosis, dogs are “staged” with various tests to look for other areas of involvement.
Treatment for dogs with lymphoma involves chemotherapy +/- surgery or radiation therapy in some cases. Generally canine lymphoma—especially multi-centric lymphoma—responds well to chemotherapy with 80-90% of dogs successfully entering a remission quickly after starting therapy. There are various treatment protocols available, and dogs generally handle treatment well having minimal to no side effects in most cases.
The prognosis for dogs with lymphoma is based on various factors that are determined at the time of diagnosis. Survival is often in the 1-2 year range for those on chemotherapy.