Lymphoma in Dogs

What Is Lymphoma in Dogs?

Lymphoma, also known as lymphosarcoma (LSA), is one of the most common cancers in dogs. LSA occurs due to an overgrowth and unregulated cellular division of lymphocytes, a type of cell that plays a crucial role in the immune system that helps protect the body from infection.

Although LSA can affect any organ of the body, it primarily affects parts of the immune system, including the lymphatic system, lymph nodes, spleen, and bone marrow. The lymphatic system is interconnected with the bloodstream, which is why LSA is considered a systemic disease and, as such, requires systemic treatment such as chemotherapy.

Types of Lymphoma in Dogs

There are several types of LSA in dogs, categorized by the organs affected. The most common are:

• Multicentric Lymphoma: first noted in the lymph nodes

• Gastrointestinal Lymphoma: affecting the stomach and intestines

• Cutaneous Lymphoma: lymphoma of the skin

Less common types of lymphoma in dogs include:

• Extranodal Lymphoma: an uncommon form that occurs when lymphoma develops in an organ outside the lymphatic system, such as an eye or kidney

• Mediastinal Lymphoma: also uncommon, but occurs when lymphoma affects the lymphoid organs within the chest cavity, such as the thymus

Symptoms of Lymphoma in Dogs

The most common symptom of LSA in dogs is an enlarged, firm, non-painful lymph node. Dogs have multiple pairs of lymph nodes throughout the body, but the easiest lymph nodes to locate and feel are the prescapular (front of chest), submandibular (under the jaw), and popliteal (behind the knees). Usually one, both, or multiple nodes are enlarged.

Dogs with LSA may also experience:

• Weight loss

• Decreased appetite

• Swelling of the face or limbs

• Increased thirst and urination

Symptoms specific to the body area affected can also include dry, crusty skin with patches of hair loss, loss of color, and ulcerated skin (cutaneous LSA); diarrhea and vomiting (gastrointestinal LSA); and exercise intolerance, coughing, and trouble breathing (mediastinal LSA).

Causes of Lymphoma in Dogs

Cancer often occurs for reasons that are not well understood. Multiple factors that have been associated with certain cancers include:

• Age

• UV damage or other environmental triggers

• Certain viruses and infections

• DNA mutations

• Genetics

There is rarely a single cause for cancer, and the development of lymphoma is no different.

How Veterinarians Diagnose Lymphoma in Dogs

In most cases, the first sign of LSA is enlarged lymph nodes. From there, your veterinarian may want to perform a cytology (when a needle is inserted into the node and cells are obtained) or biopsy (a larger needle is inserted into the node for cell collection or to obtain a chunk of tissue) of the lymph node and have the sample reviewed by a pathologist.

Once your dog is diagnosed, your veterinarian may recommend additional tests or refer you to an oncologist for further testing and treatment, including staging—to determine how far the cancer has spread. This may include chest x-rays, abdominal ultrasound, bloodwork, bone marrow aspirates, and IHC (immunohistochemistry) or flow cytometry, which helps determine the type of lymphoma.

Stages of Lymphoma in Dogs

LSA in dogs can be classified into five stages depending on the number of body systems affected:

• Stage I: Single lymph node affected

• Stage II: Multiple lymph nodes affected in a similar region

• Stage III: All lymph nodes affected

• Stage IV: All lymph nodes affected and organ involvement (spleen, liver, chest)

• Stage V: Bone marrow involvement

Treatment of Lymphoma in Dogs

Lymphoma is one of the cancers that is most responsive to chemotherapy, and remission can often be achieved in well over 50% of dogs. Dogs tolerate chemotherapy much better than people do, and the doses prescribed are often lower, with fewer side effects than expected because the goal of treatment is to preserve the quality of your dog’s life for as long as possible. Some side effects can occur, such as:

• Decreased appetite

• Lethargy

• Mild vomiting and diarrhea

Serious side effects, such as bone marrow suppression and secondary infections, can occur, but are not as common. Dogs, with few exceptions, do not lose their hair.

An oncologist can help decide the best medication or medications for your dog. There are multiple chemotherapeutic drugs used in the treatment of LSA, including:

• Lomustine

• Vincristine

• Prednisone

• Cyclophosphamide

• Chlorambucil

• L-Asparaginase

In some cases, your veterinarian may recommend removal of a lymph node or organ affected by LSA. If chemotherapy is not an option, speak with your veterinarian about the use of steroids alone. Although not a first line of treatment, prednisone can improve clinical signs and increase the comfort of your pet, if only for a few weeks.

Despite the most aggressive of treatments, LSA cannot be cured, and most dogs will relapse at some point. A second remission, though more difficult, can be achieved for some dogs. Humane euthanasia may be recommended when the cancer and its effects can no longer be controlled.

Recovery and Management of Lymphoma in Dogs

Although LSA can be treated and go into remission, the regression of cancer, it cannot be entirely cured. You can expect the cancer to return, and another round of chemotherapy—often a different protocol than previously given—will be needed to achieve remission, which can be quite difficult. The vet should continue to examine your dog frequently for signs of relapse (often seen with enlarged lymph nodes), and it’s important to follow recommendations for recheck exams and follow-up testing.

Additionally, remember that quality of life instead of quantity is the goal for your dog with LSA. The side effects and treatments are often not as severe as what is seen in human medicine, and dogs can maintain a normal, happy and positive life throughout treatment and follow-ups.