Lymphoma, also called lymphosarcoma, is a highly malignant cancer and the most common cancer of the lymph system in dogs and cats.  The good news is lymphoma usually responds well to treatment enabling us to extend the animal’s life without sacrificing  quality of life. 

Lymphoma originates from a type of white blood cell called a lymphocyte.  Lymphocytes are the primary cells of the lymph system (lymphatics) including lymph vessels and lymph nodes.  The problem occurs when something “goes wrong” with one or a small group of normal cells and they continue to divide out of control.

The cancerous cells leave the primary site and travel via the lymphatics or blood to new areas of the body.  Because the lymphatics and blood incorporate virtually every organ in the body, these cancerous cells are able to grow anywhere, which is why lymphoma is considered malignant.  The more common sites are lymph nodes, liver, spleen, bone marrow, and gastrointestinal tract, but can occur anywhere.

So, when should we be worried?  Typically, several lymph nodes will increase in size and can be seen or felt as firm bumps just under the skin.  Lymph nodes located under the jaw, in front of the shoulders, “arm pit,” groin area, and behind the knee are more easily felt. 

To confirm the diagnosis, veterinarians  take samples of the lymph nodes with a small needle causing minimal discomfort to the animal.   A biopsy may also be needed to further classify the type of lymphoma.  Additional tests, such as blood work, urinalysis, radiographs (x-rays), ultrasound, and bone marrow aspirate may also be needed in order to determine the extent or stage of the lymphoma.

Now what?  Unfortunately, lymphoma is rarely cured and treatment is intended to maintain a good quality of life for a longer period of time.  Without treatment, animals with lymphoma are expected to live an average of 4-8 weeks from the time of diagnosis. 

The most common form of treatment is chemotherapy.  Chemotherapy is generally different in veterinary medicine than in human medicine.  Because the life expectancy in dogs and cats is so much shorter than in people, treatment is intended to maintain or improve quality of life by achieving remission (appears normal and is indistinguishable from any normal animal). 

Many of the same chemotherapy drugs are used, but at lower doses; therefore, fewer side effects are seen.  It is important to note that the goal of chemotherapy is to maintain a good quality of life for the animal regardless of the duration of life. 

There are several protocols available.  The more “aggressive” protocols usually result in a longer survival time, averaging 9 to 18 months.  Less than 25 percent will be alive after two years.

It is uncommon for dogs and cats to become sick with the chemotherapy, but they may experience occasional nausea, diarrhea, and infection.  Whiskers may be lost, but hair loss is not typically significant.  These side effects are usually controllable and the chemotherapy protocol can be adjusted if needed. 

If your pet has lymphoma, veterinary oncologists and internists are available and can assist you and your veterinarian during this difficult time.

This column is provided by the faculty of the OSU Veterinary Hospital.  The large volume of questions does not allow us to directly respond to specific email questions so please watch for your answer in the column.  Email your questions for the column to This e-mail address is being protected from spambots. You need JavaScript enabled to view it and watch for your answer.

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