Lymphoma in Dogs
Lymphoma is a common cancer seen in pet dogs. It typically affects lymphoid tissues such as lymph nodes and spleen but can occur in other sites. It is more common in middle aged dogs, typically 6-9 years old. Lymphoma can affect any breed of dog but is seen more commonly in boxers, bull mastiffs, basset hounds, St Bernards, Scottish terriers, Airedale terriers and bulldogs.
Different classifications of lymphoma exist, depending on where the cancer is located. The most common type (80% of cases) is known as multicentric, and primarily affects the lymph nodes. Less commonly, lymphoma can affect the gastrointestinal tract, the skin, inside the chest cavity, or other sites such as the heart or spine.
Lymphoma is further classified based on the specific cell types affected. Up to 70% of cases are known as B-cell lymphoma, while the remaining 30% are known as T-cell lymphoma. This classification can affect the treatment we choose, and the expected response. Lymphoma can also be referred to as low, intermediate and high-grade depending on the behaviour of the cells and how rapidly they are likely to progress.
The most common symptom of lymphoma is a painless swelling of the lymph nodes. These are located throughout the body but are most visible under the angle of the jaw, in front of the shoulders, and at the back of the knees. Some dogs are still well in themselves at the time of diagnosis, while others may be lethargic, lack appetite or have weight loss. Roughly 15% of dogs with lymphoma will also have abnormally high calcium levels, due to a hormone released by the cancer cells. This causes increased thirst and urination, as well as a lack of appetite, lethargy and muscle weakness.
Dogs with gastrointestinal lymphoma often have vomiting, diarrhoea and weight loss. Dogs with lymphoma affecting the lymph tissue in the chest cavity (known as mediastinal lymphoma) may struggle to breathe as this takes space from the lungs.
The first step in any patient suspected of having lymphoma is full blood tests, including assessment of red and white blood cells and measurement of calcium levels. This shows us changes secondary to the cancer and is important to guide treatment and prognosis.
Diagnosis of lymphoma is achieved by sampling of the lymph nodes. A fine needle aspirate (FNA) involves taking a sample of cells with a needle and can be performed easily in a consultation. This is usually enough to confirm suspicion of lymphoma; however, it cannot tell us any additional information. To determine the cell type and grade of lymphoma, a solid tissue biopsy must be taken surgically. Often, a lymph node is removed in its entirety and submitted to the lab for analysis.
Depending on the case, we may wish to gather more information about the stage of disease before deciding on treatment options. This could include imaging of the chest and abdomen (x-ray and/or ultrasound), biopsy of bone marrow, and sampling of the organs such as liver and spleen. In the case of non-multicentric lymphoma, we may need to biopsy the site of the cancer, such as the intestines or skin. In these cases, it is more likely that we will perform a biopsy straight away, rather than an FNA.
Lymphoma is a systemic disease, with cancer cells spread throughout the body. As a result, we must treat the entire body to target all the abnormal cells. Lymphoma is treated using chemotherapy; however, several different protocols can be used. Broadly speaking, protocols involving several different drugs are more time-intensive and costly but carry better response rates. Your vet may wish to consult with a specialist oncologist before deciding on a treatment plan.
Most chemotherapy protocols for lymphoma involve a combination of injections in the clinic, and oral steroid tablets given at home. Chemotherapy injections may initially be given as often as weekly, but the frequency reduces as we see a response. Chemotherapy protocols can last anywhere from 4-18 months.
