What are the clinical signs of lymphoma?
In dogs with multicentric (systemic) lymphoma, the first sign of lymphoma is swelling of the lymph nodes. The lymph nodes located in the neck, chest, armpits, groin, and behind the knees are often the most visible and easy to observe. Swelling of these lymph nodes may be noted by the dog’s owner, or first noted by the veterinarian on a routine physical exam. Most of these dogs do not have any clinical signs of illness at the time of diagnosis, although they will often go on to develop signs such as weight loss and lethargy if untreated.
In the other, less common forms of lymphoma, clinical signs depend on the organ that is affected. Alimentary lymphoma causes gastrointestinal lesions, resulting in vomiting, diarrhea, and weight loss. Mediastinal lymphoma creates lesions within the chest that take up space in the chest cavity, commonly resulting in coughing and shortness of breath. The effects of extranodal lymphoma vary significantly, depending on the organ involved.
The most common initial symptom of multicentric lymphoma in dogs is firm, enlarged, non-painful lymph nodes. A lymph node affected by lymphoma will feel like a hard, rubbery lump under your dog’s skin. The most easily located lymph nodes on a dog’s body are the mandibular lymph nodes (under the jaw) and the popliteal lymph nodes (behind the knee). Other common symptoms include loss of appetite, lethargy, weight loss, swelling of the face or legs (edema), and occasionally increased thirst and urination. The photo on the left shows a dog with edema of the left rear leg. This is caused when a swollen lymph node blocks the normal drainage of fluid from the leg.
In rare instances, dogs are apparently cured of their lymphoma by chemotherapy. Unfortunately, most dogs with lymphoma will have relapse of their cancer at some point. A second remission can be achieved in a large number of dogs, but it is usually of shorter duration than the first remission. This is because the lymphoma cells become more resistant to the effects of chemotherapy as time goes on. Eventually, most lymphomas develop resistance to all chemotherapy drugs, and dogs with lymphoma die or are euthanized when the cancer can no longer be controlled with chemotherapy.
Canine lymphomas are similar in many ways to the non-Hodgkins lymphomas (NHL) which occur in humans. Canine lymphomas and NHL are nearly indistinguishable when examined microscopically, and both tumor types exhibit similar responses to chemotherapy. In 2010, NHL was diagnosed in approximately 65,000 people in the United States, and claimed approximately 20,000 lives, making it the 7th-most common cancer overall, and the 6th-most common cause of cancer-related death. It is one of the few human cancers for which the frequency of newly diagnosed cases is still on the rise. It is our hope that research in canine lymphomas conducted by the Werling Comparative Oncology Research Center (WCORC) will discover new ways of treating NHL in both dogs and humans. Our goal is to improve the outlook for dogs and humans affected with this all-too-common cancer.
Most chemotherapy drugs are given by intravenous (IV) injection, although a few are given by mouth as a tablet or capsule. Typically, an IV catheter will be placed in one of your dog’s veins to allow us to administer chemotherapy safely. A small patch of hair will be shaved over your dog’s leg where the catheter is placed.
Cutaneous lymphoma tends to appear first as dry, flaky, red, and itchy patches of skin anywhere on the body. As the disease progresses, the skin becomes moist, ulcerated, very red, and thickened. Masses in the skin can also occur with cutaneous lymphoma. Cutaneous lymphoma may progress slowly and often has been treated for several months as an infection or allergy before a diagnosis of lymphoma is made. Cutaneous lymphoma may also appear in the mouth, often affecting the gums, lips, and the roof of the mouth. Cutaneous lymphoma in the mouth is often mistaken for periodontal disease or gingivitis in its early stages. The photo on the left shows cutaneous lymphoma in the mouth of a dog. Note the very red gums and the ulceration on the roof of the mouth.
Is lymphoma common in dogs?
Lymphoma is a relatively common cancer, accounting for 15-20% of new cancer diagnoses in dogs. It is most common in middle-aged and older dogs, and some breeds are predisposed. Golden Retrievers, Boxer Dogs, Bullmastiffs, Basset Hounds, Saint Bernards, Scottish Terriers, Airedale Terriers, and Bulldogs all appear to be at increased risk of developing lymphoma. This suggests that there may be a genetic component to lymphoma, although this has not been confirmed.
There are four different types of lymphoma in dogs, varying in severity and prognosis.