Lymphoma in Dogs

Symptoms and outcomes vary in severity depending on the type, stage, and location of the lymphoma, and particularly on whether the dog is experiencing systemic signs (vomiting, diarrhea, weight loss) upon diagnosis.

The types of lymphoma are referred to as B-cell or T-cell.

The stages of lymphoma are:

• Stage 1: a single lymph node is involved
• Stage 2: more than one lymph node is involved
• Stage 3: most or all of the lymph nodes are involved
• Stage 4: most or all lymph nodes and the spleen, liver and/or mediastinum are involved
• Stage 5: bone marrow or extranodal involvement, regardless of other systems’ condition

The location of the lymphoma affects which symptoms arise:

Multicentric lymphoma: lumps under the skin that are hard, rubbery, and cause no pain are often present.

Cutaneous lymphoma: early stages appear as dry, flaky, itchy patches and progress to ulcerated, red, thickened plaques which are often mistaken for infection.

Oral lymphoma: appears as red, ulcerated tissue and is often mistaken for periodontal disease or gingivitis.

Mediastinal lymphoma: difficulty breathing due to a mass or accumulation of fluid within the chest is common.

Gastrointestinal lymphoma: symptoms such as vomiting, dark, smelly, watery diarrhea, and weight loss occur.

Dogs with lumps under the skin at the neck or behind the knees, or showing other symptoms of lymphoma, require immediate veterinary attention.

Lymphoma makes up 7 to 14% of all cancers diagnosed in dogs, making it the most common canine cancer. Lymphoma can occur at any age, but usually occurs in dogs that are in mid- to late life. In some cases, they appear to be healthy, but have developed lumps under the skin. Lumps are usually felt at the neck or behind the knee, although other locations are possible. In some cases, skin lesions or other symptoms previously mistaken for infections or other conditions do not respond to treatment, thus requiring further investigation. Dogs showing signs of lymphoma require prompt veterinary attention to begin treatment.

Genetic predisposition is known in certain breeds. These include:

• Basset hounds
• Boxers
• Golden retrievers
• St. Bernards
• Scottish terriers
• Airedale terriers
• Bulldogs

Research into the causes of lymphoma is ongoing. Current theories are exploring the role of many factors in the development of lymphoma. These include:

• Genetic predisposition
• Viral infections
• Chemical exposure
• Bacterial infections
• Medications for immune suppression
• Cigarette smoke
• Sun exposure

Determining the underlying cause is not critical to treatment.

Diagnostic tools used to confirm lymphoma include:

• Physical exam
• Blood work
• Urinalysis
• Biopsy

Once a diagnosis is reached, staging of the cancer is undertaken to direct treatment. In addition to further blood work and biopsy, diagnostic tools used to stage lymphoma include:

• X-rays and ultrasounds
• Bone marrow aspirate
• Bronchoalveolar lavages to detect tumor cells in the lungs or airways

Treatment plans include:

• Chemotherapy
• Steroid treatment
• Radiation
• Immunotherapy (monoclonal antibodies)
• Bone marrow transplant
• Surgical removal of masses
• Palliative/hospice care

In areas with veterinary research facilities, clinical trials are sometimes offered. These trials focus on new protocols, new formulations, or new drugs that may be under investigation for conditions like lymphoma.

In some cases, secondary symptoms develop as a result of treatment. Though chemotherapy does not have the same severity of side effects for dogs as it does for humans, some dogs experience loss of appetite, nausea, decreased energy levels, and mild diarrhea and/or vomiting for a few days. Most show no side effects.

In cases where chemotherapy does result in side effects, supportive care including IV fluids, anti-nausea medication, and appetite stimulants may be indicated.

Not all dogs respond to treatment for lymphoma. Life expectancy without treatment is up to 2 months from diagnosis.

Remission is often achieved within a month of steroid treatment, but is expected to last for 2 months or less without the supplementation of chemotherapy. Steroid therapy is an important part of most palliative care plans.

Prognosis with chemotherapy depends on type, location, stage of the cancer, and particularly the presence of clinical signs upon diagnosis. The goal of lymphoma treatment is long-term remission and improved quality of life, not a complete cure. Remission is the state in which tests can no longer detect cancer in the body, or in the case of partial remission, where the cancer is still present but is no longer growing. Remission is achieved in most cases and lasts on average 1 year. In 25% of cases, remission lasts for 2 years. Once recurrence has happened, further treatments are possible. Remission lengths decrease with each recurrence until the cancer no longer responds to treatment.

There are currently no measures proven to prevent lymphoma. It is shown to have breed dispositions and like most cancers, a genetic link is strongly suggested.

Lymphoma is the most common cancer in dogs.

• Chemotherapy
• Steroid treatment
• Radiation
• Immunotherapy (monoclonal antibodies)
• Bone marrow transplant
• Surgical removal of masses
• Palliative/hospice care