Lymphoma (also called lymphosarcoma or LSA) is a progressive form of cancer involving the lymphatic system. The lymphatic system includes organs and tissues of the body such as the bone marrow, lymph nodes, spleen, and other tissues that play a role in maintaining the body’s immune system and overall health.

Lymphoma in dogs is similar to non-Hodgkin's lymphoma in people, and it represents approximately 7% of all cancers that occur in dogs.

Although the disease can occur in dogs of any breed and age, it is more commonly seen in dogs between 5 to 9 years of age. Some breeds reported to have an increased risk for developing lymphoma include:

• Retrievers (Golden and Labrador)
• Basset Hounds
• German Shepherds
• Boxers
• Terriers (Scottish, Airedale)
• Poodles
• Bulldogs
• Giant Breeds including Saint Bernards and Bull Mastiffs
• Otter Hounds
• Rottweilers

The lymphatic system runs throughout the entire body, therefore any part of it can become affected. Lymphoma can affect the entire lymphatic system or it can develop as localized disease. The various forms of lymphoma include:

• Multicentric lymphoma - affecting peripheral lymph nodes, liver, spleen
• Central nervous system (CNS)
• Mediastinal - lymphatics in the chest
• Gastrointestinal - lymphatics in the gastrointestinal tract
• Cutaneous - skin

Causes

The exact cause is largely unknown. Research suggests there may be a genetic component, as some breeds seem to be more predisposed to developing lymphoma than others. However, most lymphoma cases, as with most cancers, is associated with random genetic mutations that alters cells. Lymphoma and other cancers may also be potentiated or triggered by exposures to environmental carcinogens, certain household cleaners or industrial solvents, second-hand smoke, and lawn treatments or herbicides. 

Common Signs

The signs of cancer and lymphoma can look very similar to those of other diseases, making it difficult to recognize at first. The most common finding and initial indicator of lymphoma is the enlargement of the peripheral lymph nodes in an otherwise healthy dog. Owners may notice lumps (swollen lymph nodes) which are not painful when palpated. Depending on the stage of the cancer and its location, other signs may be noticed including:

• Depression
• Profound lethargy
• Exercise intolerance
• Fever
• Dehydration
• Weight loss and loss of appetite
• Increased urination and water intake

The various forms of lymphoma can have additional signs specific to the affected organ system. The following is a short association list, in order of the most common forms of lymphoma seen in dogs:  

• Multicentric (involving multiple lymph nodes) – non-painful, enlarged lymph nodes especially under the jaw, in the armpit and groin areas, and behind the knees. There may be abdominal distension.
• Gastrointestinal (involving the lymph nodes of the gastrointestinal tract including the stomach, intestines, and rectum) – vomiting, constipation or diarrhea, weight loss, distended abdomen, bloody or dark, tarry stool.
• Mediastinal (localized to tissues in the chest cavity) –  coughing, difficulty breathing, and signs similar to heart failure.
• Cutaneous (lymphoma of the skin) – hair loss, visible bumps, itchiness, ulceration, bruising.
• CNS (central nervous system) – neurological signs including but not limited to behavior changes, circling, seizures.

Diagnosis

A thorough physical examination by the veterinarian is the most important part of the work-up.

This will be followed by several tests to check the pet’s overall health status. The laboratory tests that are commonly performed include a CBC (complete blood count), platelet count, biochemical profile, and a urinalysis. To diagnose lymphoma, the veterinarian will then obtain samples from the enlarged lymph nodes (or other suspected abnormal tissues) by performing a fine needle aspirate (FNA) and cytology to examine the tissues under a microscope.

In the event that the aspirate and cytology cannot produce a definitive diagnosis, the veterinarian may elect to do a surgical biopsy of one or more of the enlarged lymph nodes. The tissues are then sent to a histopathology lab for examination. 

When the diagnosis of lymphoma is made, it is further categorized into stages from I to V (stage V is the most severe stage). Cancer staging helps the veterinarian in making the most appropriate treatment recommendation for the pet. Other tests the veterinarian may do to aid in the diagnosis and staging of lymphoma include bone marrow aspirates, radiographs (x-rays), and/or ultrasounds. If the pet is showing neurological signs, a cerebrospinal fluid tap may be recommended.

Flow cytometry testing can help to further determine if the dog has B-cell or T-cell LSA. This is important for determining the best chemotherapy protocol to follow and also helps in providing a prognosis for the pet. 

Treatment

Chemotherapy is the treatment of choice. There are various protocols and the best options will be presented in light of the dog's health and the best decision for the pet owner and their family. Treatment protocols are always changing and new ones being developed. Most patients tolerate chemotherapy extremely well, however there may be side effects. Read more about chemotherapy and chemo FAQs.

Successful treatment results in disease remission. Remission is a temporary recovery state where there is no evidence of detectable cancer, and this is what the veterinarian or veterinary oncologist will strive to achieve.

Multi-drug Protocols - the protocols are different for B-cell and T-cell LSA.

• B-Cell LSA

The multi-drug protocol usually recommended is CHOP which includes prednisone, L-asparaginase, vincristine, cyclophosphamide and doxorubicin. Weekly treatments are given for approximately 6 weeks. The treatments are then spaced to every 2 weeks, then to every 3 weeks - to complete a total of 6 to 12 months of treatment.

• T-Cell LSA

MOPP is a multi-drug protocol that may be recommended and includes mustargen, vincristine, procarbazine, and prednisone. This protocol consists of a 2 weeks on / 2 weeks off schedule of chemotherapy for a total of 6 to 12 months.

With these multi-drug protocols, the average survival time for patients with stage IIIa or IVa lymphoma is 1 to 1.5 years. 

Single Agent Protocols 

Doxorubicin as a single IV chemotherapy agent

A total of 5 treatments are given at 3-week intervals. The average survival time is 9 to 11 months.

CCNU as a single oral chemotherapy agent

The patient is treated every 3 weeks. The average survival time is 4 to 5 months.

Prednisone as a single oral chemotheraphy agent

This pill can be administered by the pet owner at home. The average survival time is 60 days.

Prognosis

Although lymphoma is not typically considered a curable disease, the goal of treatment is to achieve complete remission allowing the pet to live a pain-free, happy life for as long as possible. Lymphoma is one of the more responsive cancers to treatment. Greater than 75% of dogs with medium to high grade lymphoma are expected to achieve a complete remission with chemotherapy. 

• Without treatment, the average survival time of dogs is one month from the time of diagnosis
• Approximately 40 to 45% of dogs live 1 year with treatment
• Approximately 20% of dogs live 2 years with treatment

The length or duration of the first remission is variable depending on the chemotherapy protocol used, but it can range from 6 to 18 months. The second remission is more difficult to achieve. Approximately 40% of dogs will achieve a complete remission with a second course of treatment. Less than 20% of dogs achieve a complete remission with a third course of treatment.

The Future

Bone marrow transplantation is available and is being used more frequently in an attempt to cure dogs with lymphoma. This therapy may hold the promise for long term remissions and cures for dogs and cats as it becomes more available.

Contributed by The Veterinary Cancer Center