Lymphoma in Dogs
One of the most common cancers in dogs, lymphoma refers to cancer of the lymph nodes or lymphatic system. Without treatment, lymphoma carries a poor prognosis, but if diagnosed early enough, chemotherapy can help your dog to have a good quality of life for several months.
In This Article
Lymphoma or Lymphosarcoma (LSA) is when abnormal lymphoid cells rapidly replicate in your dog’s lymph nodes or other organs of the body. It is one of the most common cancers reported in dogs, and can be classified by anatomic location, staging and substaging.
There are several types of lymphoma in dogs:
Multicentric lymphoma: this is the most commonly diagnosed form of lymphoma in dogs. In this type of lymphoma, your dog’s lymph nodes become enlarged and feel like firm “bumps” under your dog’s skin.
Gastrointestinal lymphoma, also known as alimentary lymphoma: this form targets the intestines and its symptoms tend to be related accordingly – such as weight loss, vomiting or diarrhea.
Mediastinal lymphoma: this form of lymphoma occurs in the chest cavity and tends to affect the thymus gland and the mediastinal lymph nodes.
Extranodal lymphoma, including cutaneous lymphoma: extranodal lymphoma affects other organs in the body, such as the kidneys or central nervous system. One of the most common forms of extranodal lymphoma is cutaneous lymphoma, which affects the skin, and may result in skin nodules, masses, ulcers or other visible changes such as flakiness, hair loss or discoloration.
The symptoms of lymphoma will vary depending on where the cancer is located. Some of the possible symptoms include:
Enlarged lymph nodes (firm “bumps” under the skin). The lymph nodes that can be palpated on a physical exam include:
Submandibular lymph nodes, located under the jaw
Prescapular lymph nodes, located in front of the shoulder
Axillary lymph nodes, located in the armpits
Popliteal lymph nodes, located behind the knee
Inguinal lymph nodes, located in the inner thigh
Swelling of limbs (edema)
Increased water intake and urination
There is no known cause for lymphoma. Researchers have investigated chemical exposure and environmental factors, infectious organisms, genetics, as well as suppression of the immune system. However, the exact cause remains unknown.
Lymphoma can be seen in younger dogs (juvenile-onset lymphoma), however, it is more common in middle-aged to older dogs.
Any dog breed may develop lymphoma, but some are more susceptible than others. Predisposed breeds include Basset Hounds, Bull Terriers, Golden Retrievers, St. Bernards, Boxers, and several others.
Your veterinarian might diagnose lymphoma by aspirating the enlarged lymph nodes (taking a small sample with a needle) and submitting them to the laboratory for a cytology test. If lymphoma is confirmed, your veterinarian will recommend staging as well as a consultation with a specialist oncologist. Staging is the process of determining if, and where, the cancer has spread. It can also help determine how aggressive the cancer is.
Some of the tests that your veterinarian might recommend include:
Full blood work including chemistry and blood count as well as urinalysis
Calcium level testing
Chest radiographs (x-rays)
Aspirates of the spleen or liver
Molecular testing to assess specific cancer cells
Molecular testing can determine whether the lymphoma is composed of B-cells or T-cells, which is important in determining prognosis. Dogs with T-cell lymphoma have a poorer prognosis than dogs with B-cell lymphoma. T-cell lymphoma is often associated with elevated calcium levels (hypercalcemia), which carries a poor prognosis as well.
Based on the staging tests, lymphoma can be classified into 5 stages. These are:
Stage One: a single lymph node is involved
Stage Two: multiple lymph nodes in one area of the body are involved
Stage Three: all lymph nodes are involved
Stage Four: all lymph nodes as well as liver, spleen, or chest are involved
Stage Five: bone marrow involvement
Lymphoma can be further categorized into substages, which simply describes whether or not they are experiencing symptoms. Substage A does not show any symptoms, whereas substage B does.
Much like in humans, the treatment of choice for lymphoma in dogs is chemotherapy. The most common protocol is a University of Wisconsin protocol (UW-25) based on CHOP, which stands for cyclophosphamide, doxorubicin, vincristine, and prednisone. This protocol involves weekly injections of chemotherapy drugs as well as daily oral steroid (prednisone) administration. Additional treatments may include surgery, radiation, bone marrow transplants or immunotherapy.
It is important to remember that dogs do not suffer that same side effects of chemotherapy as humans do. While their white blood cell counts may decrease, they are unlikely to experience the severe nausea, inappetence, fur loss, and malaise reported by human chemotherapy patients.
Is there a cure for Lymphoma in dogs?
There is no cure for canine lymphoma. The goal of treatment is to get your pet into remission (a disease-free state) for as long as possible and to give them a good quality of life.
Is Lymphoma contagious to humans or other pets?
No. Lymphoma is not contagious to humans or other pets.
What is the cost of treating Lymphoma in dogs?
The diagnostic and staging tests can amount to hundreds or thousands of dollars. If chemotherapy is elected, the cost will certainly reach thousands of dollars. With chemotherapy, your dog will require weekly visits to the oncologist as well as blood work prior to administration of chemotherapy medication. If prednisone treatment is elected, the medication is not expensive.
Your pet’s prognosis will vary greatly depending on the type of lymphoma that they have, including its staging and substaging, so it’s difficult to give a specific prognosis. However, as an average, the median survival time for dogs who undergo treatment for high-grade B-cell lymphoma with the CHOP protocol is 9-13 months (compared to approximately 6 weeks without chemotherapy). The median survival time for dogs undergoing treatment for high-grade T-cell lymphoma is reported to be 5-9 months.
While Lymphoma cannot be cured, getting your pet into remission can help them to enjoy their remaining time. Remission may be complete or partial. In complete remission, all of the signs of disease disappear. In partial remission, the signs decrease by at least 50%.
It is impossible to predict how long your pet will remain in remission. Once remission is lost, the lymph nodes will become enlarged again, and at this point, your pet’s chemotherapy protocol will be adjusted as the original drugs are no longer effective. The new protocol is called a “rescue protocol.”
If chemotherapy is not elected, your pet will be treated with steroids. In this case, they might enter remission after the first month of treatment. However, remission is short-lasting and usually lasts one to two months.
Given that we do not know the cause of lymphoma, there is not much that can be done in terms of prevention. Reduction of exposure to chemicals and toxins is recommended.
Is there a vaccine for Lymphoma in dogs?
No, there is no vaccine to prevent lymphoma. However, immunotherapy may be provided in the form of a vaccine in addition to chemotherapy while treating lymphoma.
The most common type of lymphoma in dogs is multicentric lymphoma, which is characterized by enlarged lymph nodes. While the long-term prognosis is poor, treatment can give your dog a few months of a good quality life. It is important to take your dog to your veterinarian if you ever find new “bumps” on him. In general, senior dogs should be examined by your veterinarian twice yearly. Your veterinarian assesses your pet’s lymph nodes for size and symmetry during every examination and can catch concerning changes early.