January 1, 2001 (published) | September 2, 2021 (revised)

Lymphoma, also called lymphosarcoma, is a highly malignant tumor of the lymph system.
It is one of the most common forms of cancer in both humans and small animals.

Presumably you are here because your pet is suspected of having this form of cancer. Perhaps the diagnosis has already been confirmed. In either case, you want to know more and there turns out to be much more to know. Because lymphoma is a common form of cancer in humans, research and new development in this area abounds. Animal patients as well as human patients have benefitted from this research.

What is the Lymph System?

The lymph system is a network of lymphatic vessels and lymph nodes through which foreign proteins and disease organisms are circulated. The lymph nodes serve as processing centers where these foreign substances may be presented to the cells of the immune system. There are many different types of immune-related cells; some produce antibodies, some circulate and destroy the foreign materials they encounter, and some regulate the activity of other cells.

Lymphocytes are the primary cells of the lymph system and they act in the various ways mentioned. The lymph vessels serve as a circulatory path for lymphocytes in addition to serving as a collection system directing foreign substances toward the lymph nodes. Lymph vessels interface with the blood stream at several areas allowing lymphocytes greater area to patrol. In many ways, the lymph system is similar to a second circulatory system in the body, one that circulates lymph fluid instead of blood.

What is Cancer?

Cancer occurs when a normal cell “goes wrong.” The cell’s normal regulatory processes disengage and it begins to divide quickly and without control. These cells do not stop at barriers, nor do they stop growing when they outgrow their own blood supply. They divide over and over, taking over local tissues and escaping to spread to other body areas. The organ to which the original cell belonged is destroyed as the cancer cells obliterate its structure. Other local tissues may also become invaded as the tumor cells grow inexorably into them.

Cancer cells break off the primary tumor and travel via blood or lymph vessels to new areas of the body. Wherever these cells lodge, they may start new tumors far from the original tumor but just as deadly. This process continues until there is not enough normal tissue left to sustain life. This form of cancer spread is called metastasis.

What is Lymphoma?


Malignant lymphocytes readily travel through the lymph vessels to other nearby lymph nodes. When nearby nodes have been infiltrated, the cancerous lymphocytes continue their journey through the lymphatic system to distant lymph nodes. Soon all the nodes are enlarged. Other organs that harbor lymph tissues (liver, spleen and even the GI tract) can become infiltrated. Ultimately, the bone marrow, where most blood cells are formed, is affected, the immune system is destroyed, and severe anemia and weakness claim the victim's life.

Without treatment, animals with lymphoma are expected to live 4-8 weeks from the time of diagnosis.

Most patients (especially dogs) are not feeling particularly sick at the time of diagnosis. It may be tempting to hold off on treatment until the pet seems more ill. Waiting can drastically reduce the chance for long-term survival; better remission quality is obtained if the patient is treated while he/she still feels healthy.

What is Staging?

Cancer, including lymphoma is staged depending on how many body areas are involved. The more localized the cancer is, the lower the stage. The more areas are involved, the higher the stage. The stages of lymphoma are:

Stage I: involvement of a single lymph node
Stage II: involvement of lymph nodes on only one side of the diaphragm (in either only the front half or only the back half of the body)
Stage III: generalized involvement of peripheral lymph nodes, including both the cranial (above the waist) and caudal (below the waist) halves of the body
Stage IV: involvement of liver and/or spleen
Stage V: involvement of bone marrow, central nervous system or some other unusual location.

The good news is that response to treatment in lymphoma is not affected by stage until the last stage is reached.

Lymphoma staging also involves substaging, which includes determining if the patient is feeling healthy (substage A) or sick (substage B). Substage A carries a much better prognosis and response to treatment versus substage B.

Obviously everyone wants to find their pet has potential for a long remission. This will mostly be determined by the what body part is involved, whether the patient feels sick or not, whether there are additional secondary problems (such as kidney failure as in renal lymphoma, or elevated blood calcium levels), and whether prior treatment might have made the tumor resistant to other treatments.

What is Remission?

Remission is the state where cancer is not detectable in the patient and the patient feels completely normal. (Note that this state is different from a cure, where the cancer is considered to be gone forever.) Prolonged remission is the goal of cancer therapy which, for most lymphoma cases, means chemotherapy. This may sound intimidating but chemotherapy for pets is not the same experience as it is for humans. For example, nausea and hair loss are generally uncommon for pets. Keep in mind that humans want a remission measured in decades if possible and most pets only need several years. This makes chemotherapy a different experience for pets.

For any patient, there is an approximately 75% chance of achieving remission no matter which protocol is used.

Because lymphoma cells are quite sensitive to chemotherapy medications, there is an excellent chance of reducing the tumor to undetectable levels. How long a remission lasts depends on what protocol is used and a number of other factors. To learn more about where your pet fits into the statistics, please review the section on lymphoma in your pet's species. Numerous protocols are available and there is one to potentially fit every budget and every schedule.

What is the Cure?

Cure is the permanent removal of all traces of tumor such that no further treatment is needed. In effect, it is a permanent state of remission. While this is technically possible for your pet, it is more constructive and realistic to focus on increasing life quality. With lymphoma, remission is likely but cure is not. Treatment may be thought of as an exchange of only a short time with your pet for a substantially longer time with your pet. It is important to keep your goals in proper perspective through this treatment: In veterinary medicine, the goal for lymphoma is a long remission, not a cure.

