Lymphoma in dogs is rather common, making up about 7 to 25 percent of all dog cancers. It typically occurs in the lymph nodes, although it can occur in other parts of the body as well.
Canine lymphoma (or canine lymphosarcoma) is a malignant cancer of the lymphocytes. (Lymphocytes are cells in the lumphatic system which are responsible for mounting an immune response. Two main types are B cells and T cells.)
About eighty percent of all cases of canine lymphoma is the multicentric form, in which different parts of the body are attacked by cancer cells that use the lymphatic system to spread.
As you can imagine, because the lymphatic system has "tubes" connecting the whole body, lymphoma cancer cells can spread easily because they are highly mobile.
Lymphoma can occur in:
Lymphoma can also occur in other less common sites in dogs, such as the bone marrow, the nervous system, nasal cavity, or kidneys.
The cancer can be aggressive and can rapidly ruin the health of the internal organs. If left untreated, it can become life threatening to the dog patient in less than eight weeks.
Lymphoma is a common cancer among dogs, making up approximately 7 to 25% of all canine cancers. It occurs more commonly among middle-aged to older dogs (between 5-9 years of age).
Clinical signs depend on the location of the tumor(s), and the extent to which the disease has developed.
For tumors that occur in the lymph nodes, we can notice a painless enlargement of the dog patient's lymph nodes, with no other symptoms.
The enlarged lymph nodes can be felt, as mentioned above, most commonly under the jaws. However, lymph nodes in other parts of the body (around the area of the shoulder, the back of the leg, behind the knee joint, and in the groin area) can also be swollen.
The swollen lymp nodes are firm and are freely moveable beneath the skin. The dog usually does not feel sick.
Sometimes the affected lymph nodes will enlarge, then shrink back to normal size, then enlarge again. The enlarged lymph nodes can be 5 to 10 times bigger than normal size.
For lymphoma that occurs in the stomach or intestines, the dog patient may show signs that are typical of gastrointestinal problems, such as:
Lymphoma that occurs in the skin can present itself in several different ways, including single or multiple lumps in the skin, or mouth. These lesions can be red, itchy, and ulcerated.
The exact cause is unknown, although there seems to be increased risk in dogs who have been exposed to the herbicide 2,4-D. Other possible causes include exposure to strong magnetic fields, or genetic predisposition.
In addition, age seems to be a risk factor for lymphoma in dogs. Lymphoma occurs more commonly among middle-aged to older dogs. In fact, most affected dogs are between 5-9 years of age.
Breed-wise, the following breeds of dogs tend to have a higher risk of developing canine lymphosarcoma:
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Depending on the location of the tumor, canine lymphoma is diagnosed using a combination of tests, such as blood tests, fine needle aspirates of the tumor, biopsies, x-rays and ultrasound.
Since lymphoma in dogs is considered a systemic or whole body disease and may strike in any location, surgery is ineffective and impractical.
The treatment of choice is chemotherapy which usually consists of a combination of oral and injectable drugs given on a weekly basis.
Some commonly used anticancer medications for canine lymphosarcoma include Elspar, Cytoxan, Oncovin, Adriamycin, and prednisone.
While undergoing chemotherapy, regular blood tests should be carried out to monitor for decreased white blood cell counts (drug-induced myelosuppression).
For the same reason as surgery, radiation is not commonly recommended for lymphoma in dogs. However, relatively novel approaches have recently been adopted to treat canine lymphosarcoma.
For example, the dog patient may receive half-body irradiation - each half body is treated 4 weeks apart. Also, radiation to a single lymph node or all nodes may be given to dog patients that are drug-resistant.
Most dogs with lymphoma are rather responsive to chemotherapy. Greater than 75% of dogs with lymphoma are expected to achieve a complete remission of 6 to 11 months with chemotherapy.
When a dog treated with chemotherapy comes out of remission, further chemotherapy (rescue protocol) can be given which may induce second or even third remissions.
However, understand that cancer cells that have survived prior chemotherapy treatments are stronger and more resistant to being eradicated. So, stronger and stronger medications have to be used.
Dog parents, at that stage, have to make a decision as to whether it is in their dogs' best interest to have more rounds of treatment or whether euthanasia is a better option.
Update: Bone marrow transplant treatment is now available for dogs with lymphoma. Visit this page for more information.