Most of us have heard of lymphoma. It is a common cancer in people and dogs, which does not make it any less terrifying for dog owners receiving a canine lymphoma diagnosis. Understanding lymphoma can help owners come to terms with a dog's condition, assisting us in making more informed decisions about our dog's health.
Here are the symptoms, diagnostic procedures, treatment options, and prognosis statistics you need to know about lymphoma in dogs.
What Is Lymphoma?
Canine lymphoma is similar to non-Hodgkin’s lymphoma in people. It is so similar, in fact, that veterinarians and human doctors use almost the same chemotherapy protocols to treat lymphoma in their patients.
Scientifically speaking, lymphoma is a blanket term used by doctors to describe a group of cancers that stem from the lymphocytes. Lymphocytes are a type of white blood cell that helps the immune system fight off infection. They are highly concentrated in organs that play a role in the immune system, like the lymph nodes, the spleen, and bone marrow. While lymphoma can affect any organ in the body, these organs tend to be where most lymphoma cancers are found.
Types of Lymphoma
There are more than 30 different types of known canine lymphomas, all of which vary in aggressiveness, survival rates, and clinical signs. The four most common types of lymphoma in dogs that owners should know about are:
- Multicentric lymphoma
- Alimentary lymphoma
- Mediastinal lymphoma
- Extranodal lymphoma
Multicentric lymphoma is by far the most common of these types. Approximately 80 to 85 percent of lymphomas in dogs is multicentric. This type of cancer affects the lymph nodes, and in the majority of cases, the most obvious clinical manifestation is the rapid enlargement of the lymph nodes.
The second most common form of lymphoma is alimentary lymphoma, which accounts for less than 10 percent of canine lymphomas. Alimentary lymphoma targets the intestines, which is where the majority of symptoms occur.
Mediastinal lymphoma is rare. In this disease, either or both the thymus and the mediastinal lymph nodes in the area of the chest become enlarged, caused by high-grade malignant T lymphocytes.
Extranodal lymphoma in dogs refers to lymphoma that targets a specific organ, such as the skin, eyes, kidneys, lungs, or central nervous system. The most common extranodal lymphoma affects the skin and is called cutaneous lymphoma.
What Causes Lymphoma in Dogs?
There is still so much we don't know about cancer. Scientists currently do not know what causes lymphoma in dogs, but there is hope that advanced genetic studies will eventually help identify any underlying genetic and chromosomal causes and predispositions. What we do know is that dogs share our environment, and so they are exposed to many of the same cancer-causing environmental factors as we are, including toxic substances like phenoxyacetic acid herbicides and magnetic field exposure.
Symptoms of Lymphoma in Dogs
The symptoms of lymphoma in dogs are as varied as the different types of lymphoma, which can make it difficult to diagnose at first.
Symptoms: Multicentric Lymphoma
The first symptom that dogs with multicentric lymphoma usually show is swollen lymph nodes. It is common for dogs with lymphoma to have lymph nodes 3-to-10 times their normal size. These swellings are not painful and feel like a firm, rubbery lump that moves freely beneath the skin. Dogs with multicentric lymphoma may also develop lethargy, fever, anorexia, weakness, and dehydration as the disease progresses.
Symptoms: Alimentary Lymphoma
Dogs with alimentary lymphoma, which affects the intestines, may present with vomiting, abdominal pain, anorexia, diarrhea, and weight loss.
Symptoms: Mediastinal Lymphoma
Dogs with mediastinal lymphoma typically have difficulty breathing. This may be due to the presence of a large mass within the chest or due to the accumulation of fluid within the chest (pleural effusion). Affected dogs may also show swelling of the face or front legs as well as increased thirst and urination.
Symptoms: Extranodal Lymphomas
The symptoms associated with extranodal lymphomas depend on the organs affected. Cutaneous lymphoma, the most common type, affects the skin. Telltale signs of cutaneous lymphoma are individual, raised nodules or more generally dispersed scaly lesions. Cutaneous lymphoma may also appear in the mouth, often affecting the gums, lips, and the roof of the mouth.
If the extranodal lymphoma is in the lungs, symptoms of respiratory distress are likely. Similarly, extranodal lymphoma in the kidneys could cause renal failure, lymphoma in the eyes can cause blindness, lymphoma in the central nervous system can lead to seizures, and lymphoma in the bones can cause pain or fractures.
Diagnosing Lymphoma in Dogs
Once cancer is a suspected, veterinarians get a definitive diagnosis by taking a sample of the affected organ. The most common diagnostic tool is something called a fine-needle aspiration, which extracts a sample of a dog’s lymph nodes or organs to be evaluated through cytology exam or by a histopathologic tissue evaluation.
Some veterinarians recommend “staging tests” following a lymphoma diagnosis to determine how far the disease has progressed throughout the dog’s body. These tests help veterinarians understand your dog’s overall condition, as well as the cancer, and include blood tests, urinalysis, x-rays, abdominal sonograms, and bone marrow aspiration.
Treating Lymphoma in Dogs
The treatment therapy proven most effective for canine lymphoma is chemotherapy. The type of chemotherapy your vet recommends will vary depending on the type of cancer, and in some cases the vet may also suggest radiation therapy or surgery. For instance, dogs with multicentric lymphoma are often given the chemotherapy protocol UW-25, which is based on the CHOP protocol used in humans, whereas the chemotherapy protocol thought to be most effective at treating cutaneous lymphoma is lomustine (CCNU).
When it comes to chemo, dogs have a better deal than their owners. Chemo does not usually make dogs as sick as it does people, and dogs rarely lose their hair—with the exception of (but not limited to) these breeds: Poodles, Old English Sheepdogs, and the Bichon Frise. The most common side effects of chemotherapy in dogs are mild vomiting and diarrhea, decreased appetite, and decreased activity levels.
Canine Lymphoma Prognosis
Perhaps the most important question dog owners want answered about canine lymphoma is the survival rate. We want to know how long a dog diagnosed with lymphoma has to live, so we can know how to react emotionally and make the appropriate arrangements for our dog's care.
The answer, unfortunately, is not that simple. Lymphomas vary widely in their aggressiveness, and the prognosis will also depend on the stage of your dog’s cancer at the time of treatment and the choice of treatment itself.
Owners also need to know the difference between the terms "remission" and "cure." Total remission means that all signs and symptoms of cancer have disappeared, but cancer could still be in the body. Partial remission means that some, but not all, signs and symptoms of cancer have disappeared. Remission, however, is different from a cure, which can be defined as elimination of the disease entirely.
Dogs in remission usually still have cancer; it is just undetectable for the time being. Treatment can buy your dog some time, but it rarely cures the disease and unfortunately most dogs with lymphoma will have a relapse at some point. When the cancer returns, it is more resistant to treatment, although a second remission can be achieved in some cases. Eventually, however, lymphoma is fatal.
Living With Canine Lymphoma
No owner wants to hear that their dog has lymphoma, but there are steps owners can take to help you and your dog after diagnosis. Talk to your vet about the available treatment options and about what to expect as the disease progresses. Discuss the possibility of hospice care for your dog and what you can do to keep him comfortable.
Being proactive about your dog’s cancer improves his quality of life by helping you accept your role in his treatment program. End of life discussions are hard, but they only get harder as time goes on.
Lymphoma is a complex disease with many different factors that can impact your dog's health. If you are worried your dog might have lymphoma, or if you have more questions about your dog's cancer, call your vet.