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What is Canine Lymphoma?

By Dr. Lillie Davis, DVM, DACVIM (Oncology) and Dr. Suzanne Rau, DVM, DACVIM (Oncology) | Oncology

Canine lymphoma is one of the most common forms of cancer seen by the oncology department. Lymphoma originates from a type of white blood cell in the dog called a lymphocyte. Today Lillie Davis, DVM, DACVIM (Oncology) and Suzanne Rau, DVM, DACVIM (Oncology) walk us through the symptoms, diagnosis, and treatment of canine lymphoma.

What is lymphoma?

Lymphoma is a cancer originating from lymphocytes, one type of white blood cell in the body. Lymphocytes normally are found in the highest quantities in lymph nodes throughout the body, and function as part of our immune system to fight infections.

When one of these lymphocytes transforms and becomes cancerous, the cells replicate and lead to the formation of lymphoma. Canine lymphoma manifests as enlarged lymph nodes in the majority of dogs, but can also spread to or originate in other areas in the body, including the liver, spleen, and bone marrow.

What are common types of lymphoma?

Lymphoma in dogs can be categorized in several ways. One method of categorization is based on the locations of the lymphoma. Multicentric lymphoma, involving multiple lymph nodes throughout the dog’s body, is the most common form. Lymphoma can also be primarily related to the gastrointestinal tract, skin (cutaneous), liver (hepatic), spleen (splenic), and as a mass sitting in the chest in front of the heart (cranial mediastinal) among other locations.

Lymphoma can also be categorized based on cell type (also called immunophenotype). The two most common immunophenotypes of lymphoma are B cell and T cell lymphoma. In general, for high grade (or large cell) multicentric lymphoma, B cell lymphoma carries a more favorable outcome with therapy, while T cell lymphoma can still respond, but tend to have shorter remission durations and survival times with treatment.

Lymphoma is also classified by grade, or level of aggressiveness. High grade lymphoma, usually described as larger lymphoma cells, is most common. Low grade lymphomas, usually with smaller lymphoma cells, are also possible, though less common. Low grade lymphomas have a more indolent course, meaning they usually are slower to progress. If a low-grade lymphoma is suspected, a special test called a flow cytometry may be recommended to further investigate this possibility.

What are the symptoms of lymphoma?

Most dogs with lymphoma present to the hospital feeling well, without signs of sickness. Usually a client palpates enlarged masses in the neck region. On further evaluation by their veterinarian, these masses are determined to be enlarged lymph nodes. Further sampling of the lymph nodes then confirms lymphoma. Less commonly, a dog may feel sick when the lymphoma is found. Clinical signs are nonspecific, and may include any combination of inappetence, lethargy, vomiting, diarrhea, and trouble breathing.

How can a pet owner detect lymphoma?

The most common way a pet owner can detect lymphoma is to feel their dog for any new lumps and bumps. If any new masses are found, they should be checked by a veterinarian. Enlarged lymph nodes can be located in the neck region under the chin, in front of the shoulders, in the armpits, in the groin, or behind the knee.

How can lymphoma be diagnosed?

Diagnosis of lymphoma is usually achieved by cytology or biopsy or an enlarged lymph node or other abnormal organ or mass. Cytology involves using a needle to obtain an aspirate sample of cells from the area of concern, and placing them on a slide. The slide is then sent to the pathologist, who evaluates the cells. Biopsy involves taking an actual tissue sample from the area of concern, and submitting it to the pathologist for histopathological evaluation. In certain instances, additional testing with PARR (PCR testing) and/or flow cytometry may be recommended or necessary to obtain a diagnosis.

What is the treatment for lymphoma?

The treatment for lymphoma varies depending on the lymphoma location and type. Typically, though, it involves some regimen of chemotherapy along with an oral steroid, like prednisone. Several protocols exist for the different types of lymphoma. The pros and cons of each protocol are discussed with a client prior to making a decision to pursue treatment. The most standard protocol for a high grade multicentric lymphoma would be a CHOP protocol. This is a multiagent protocol involving about 16 treatments over the course of 20-25 weeks. There is an approximately 85 percent response rate with this protocol, and the prognosis varies depending on the lymphoma type. Protocols involving fewer drugs and less treatments also exist, though the efficacy is generally lower with these protocols.

In general, dogs tolerate chemotherapy quite well, often better than their human companions. Still, side effects are possible, and can include stomach upset 3-5 days after treatment, as well as a drop in the white blood cell count about one week after treatment. While side effects are generally mild and can be treated at home with supportive oral medications, they can be more severe in about 5% of dogs, requiring a return to the hospital for supportive care.

What is the difference between remission and cure for lymphoma?

For canine lymphoma, we most often achieve remissions rather than actual cures. A remission is when treatment makes the cancer clinically undetectable. This means that physical exams, imaging, and lab work all appears normal, and we can no longer find evidence of the lymphoma. However, most patients will relapse in the future, meaning that the cancer is likely still present, but at an undetectable level.

What is the prognosis for lymphoma in dogs?

There is not a simple answer to this question. The prognosis will vary based on the type of lymphoma, as well as the treatment elected by the owner. It is best to discuss your dog’s lymphoma with an oncologist to help determine the potential prognosis with various treatment options. For our most common high grade forms of multicentric lymphoma, the prognosis without treatment is often short, in the range of four to six weeks. This is a quickly progressing cancer, and dogs can quickly become sick as the cancer spreads throughout the body. When treated with our best CHOP chemotherapy protocol, the prognosis is an average of 12-16 months for B cell lymphoma, and six to nine months months for T cell lymphoma. When treated with prednisone, a steroid, alone, the prognosis is about six to eight weeks.

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