4 Australian Shepherds running in the park.

Lymphosarcoma (Lymphoma) in Dogs

Lymphoma is a malignant cancer that affects dogs and consists of malignant lymphocytes, which are a type of white blood cell in the body. It can take up residence in any tissues where lymphatics or lymphocytes are present. In a healthy animal, the lymphoid system is an important part of the immune system’s defense against infectious agents, such as viruses and bacteria.

Lymphoid tissue is normally found in many different parts of the body, including the lymph nodes, liver, spleen, gastrointestinal tract, and skin. Lymphoma is the most common hematopoietic cancer for canines, and it accounts for 7-14% of all cancers diagnosed in dogs. Canine lymphoma is similar to non-Hodgkin’s lymphoma (NHL) in humans, and, microscopically, the lymphocytes look similar in both NHL and canine lymphoma. NHL is the 7th most common type of cancer diagnosed in humans.

Canine lymphoma is caused by a population of lymphocytes that are cancerous and are either B or T-cell immunophenotype. It is further classified beyond its immunophenotype based on its location.

Types of Lymphoma in Dogs

Lymphoma can occur in dogs of any age, but is most commonly seen in aging dogs. Breeds that are at a higher than average include Rottweilers, Scottish Terriers, Boxers, Golden Retrievers, Basset Hounds, and German Shepherds. Males and females are affected equally. There may be a genetic basis for this disease in Boxers, Cocker Spaniels, and Irish Setters. Further research showed that Boxers tended to develop more aggressive T-cell based lymphoma, while Rottweilers and German Shepherds tended towards B-cell immunophenotypes.

Clinical Signs

Clinical signs in dogs with lymphoma are highly variable depending on the location of the cancer and progressiveness of the disease. Some dogs will have multiple, vague clinical signs, while others will only have enlarged lymph nodes.

Clinical signs include:

Diagnosis of Lymphoma in Dogs

If lymphoma is suspected in a patient, a complete medical history and physical exam is completed by a veterinarian. Based on these findings, further diagnostic tests are needed to recognize lymphosarcoma and exclude other diseases.

Tests may include:

Treatment of Lymphoma in Dogs

The goal for treatment of canine lymphoma is clinical remission, which means resolution of clinical signs and maintenance. Curing lymphoma is often not possible, so the goal is to remain in remission for as long as possible.

Treatment for lymphoma may include the following:


Chemotherapy is the most commonly recommended treatment for dogs with lymphoma. A dog is said to be in remission when clinical evidence of the cancer disappears after treatment. Achievement of remission by chemotherapy does not mean that the animal is cured, and cancer is likely to return if treatment is discontinued. The most common chemotherapy protocol for canine lymphoma is called CHOP.

Commonly used drugs include:

Depending upon the drug, treatment can be given by injection under the skin (subcutaneously), intravenously, or orally. Combinations of these drugs work better than a single drug protocol.

Chemotherapy is very successful in dogs with lymphoma. Initial treatment success rate in dogs that receive aggressive chemotherapy is >90%. Working with an oncology team to create an individualized treatment plan is highly recommended.

An oncologist’s protocol may include:

Side Effects of Chemotherapy

The most common adverse effects of cancer chemotherapy are gastrointestinal symptoms (loss of appetite, vomiting, diarrhea) or a decreased white blood cell count, which may increase the risk of secondary infection. Dogs generally do not experience the hair loss that affects humans undergoing chemotherapy. In fact, dogs usually tolerate chemotherapy much better than humans. The risk of a serious adverse effect that would require hospitalization is small (perhaps 5 to 10%). If adverse effects do occur, your veterinarian may change the protocol to prevent them during future treatments.

Eighty to 90% of dogs treated for lymphosarcoma by chemotherapy achieve remission, and average survival time is one year with B-cell lymphoma and 6 months with T-cell. Ten to 15% of dogs treated for lymphosarcoma survive 2 years or more.


In serious cases, an oncologist may recommend either whole body radiation or half body radiation. This is commonly used in conjunction with chemotherapy and can extend disease-free intervals. An oncologist will also create a radiation protocol similar to chemotherapy protocol. This includes how many treatments are recommended, how far they are spaced out, what sedation/anesthetic protocol would be used for treatment, and a list of facilities where chemotherapy is being administered (if unavailable).

Radiation therapy requires referral to a specialty institution with specialized equipment and training. It may be recommended if an animal has lymphosarcoma localized to a single site. It is essential, in this situation, to conduct a thorough search for other areas of involvement. Chemotherapy should be used in conjunction with radiation therapy if other areas of involvement are suspected.

Adverse effects vary depending upon the region of the body treated and the number of treatments given. Animals must be anesthetized for each treatment to prevent movement during radiation exposure. Treatment of one-half of the body has been used in dogs that have come out of remission. If a good response is obtained, the other half of the body is treated 3 to 4 weeks later. Adverse effects from this type of radiation therapy are similar to those observed after chemotherapy and include gastrointestinal symptoms and low white blood cell counts.
Radiation can also be used if lymphosarcoma is present in a specific location of the body that shows signs of discomfort or other clinical signs. This type of treatment is called palliative radiation therapy, and involves use of a few large doses of radiation to the affected area. Adverse effects are minimal with this type of radiation therapy.


It often is possible to treat pets successfully a second time using different drugs or radiation therapy when relapse occurs. Different treatment approaches are necessary because the malignant lymphocytes have become resistant to the previous drug regimen. It is more difficult to treat animals experiencing a second or third relapse, and remission times generally are shorter.

Palliative Care

Lymphoma can also be managed without chemotherapy and/or radiation through at-home corticosteroid treatment. This can be successful for short-term treatment when further advanced treatments are declined or failing. Treatment success rates are much lower with this treatment, but they can be far more expensive. Long-term prognosis is usually <3 months with just corticosteroid treatment.

Follow-Up Care for Dogs with Lymphoma

Promptly seek veterinary care if your dog develops vague signs of illness (loss of appetite, lethargy, unexplained weight loss) or abnormal swellings under the skin of the neck, shoulders, armpits, or thighs.

Dogs that are under the care of an oncologist for treatment of lymphoma may have transient gastrointestinal upset or decreased appetite. Working with your veterinarian to create the best medication plan to manage these clinical signs is essential. This often involves managing their nausea and using appetite stimulants to counteract reduced appetite.

White blood cell count may decrease after chemotherapy and increase the risk of secondary bacterial infection. Signs to watch for include lethargy and loss of appetite. A rectal thermometer can be used to monitor temperature at home. A temperature of greater than 102.5°F in an animal that is lethargic is cause for concern. Seek veterinary care promptly if you think your pet has an infection. Hospitalization to provide fluid therapy and intravenous administration of antibiotics may be necessary. Your veterinarian will monitor your dog’s white blood cell count during chemotherapy and may adjust drug dosage or schedule.