Lymphoma is one of the most common cancers seen in dogs.  Although there are breeds that appear to be at increased risk for this disease, lymphoma can affect any dog of any breed at any age. It accounts for 10-20% of all cancers in dogs.

Lymphoma (lymphosarcoma or non-Hodgkin's lymphoma) is a malignant cancer that involves the lymphoid system. In a healthy dog, the lymphoid system is an important part of the body's immune system defense against infectious agents such as viruses and bacteria. Lymphoid tissue normally is found in many different parts of the body including lymph nodes, liver, spleen, gastrointestinal tract and skin. Lymphosarcoma is classified according to the location in the body in which the cancer begins.

These include:

  • Multicentric form occurs in the lymph nodes.
  • Gastrointestinal form occurs in the stomach, intestines, liver and lymph nodes in the abdomen.
  • Mediastinal form occurs in the mediastinum, in front of the heart in an organ called the thymus. 
  • Hence this form of lymphosarcoma sometimes is called thymic lymphoma.
  • Cutaneous form occurs in the skin.
  • Acute lymphoblastic leukemia occurs when the disease starts in the bone marrow.
  • Miscellaneous forms of lymphosarcoma are less common and include those that begin in the
  • Nervous system, nasal cavity or kidneys.


While we understand how lymphomas form, we still do not understand why. There is growing evidence and much speculation that environmental factors such as exposure to pesticides (especially herbicide 2,3-D) (Read New York Times Article:  Lawn Herbicide Called Cancer Risk for Dogs) . A new study published in April 2012 finds that utilizing a chemical lawn service to achieve a lush lawn is likely causing malignant cancer in many pet dogs.  In the study, researchers identified 263 dogs with biopsy-confirmed canine malignant lymphoma (CML), 240 dogs with benign tumors, and 230 dogs undergoing surgeries unrelated to cancer. Then, they asked the pet owners to complete a 10-page questionnaire. Scientists found that dogs with malignant lymphoma were 70 percent more likely to live in a home where professionally applied lawn pesticides had been used. 

Dogs with the serious malignancy were also 170 percent more likely to come from homes where owners used chemical insecticides to combat pests inside of the home.

There is some speculation that strong magnetic fields may increase the incidence of lymphoma in dogs, but there is currently no absolute proof of this. Evidence has emerged of a possible genetic correlation in dogs because of the higher prevaience of lymphoma in certain breeds, but further studies need to be performed to determine the exact risk factors involved in canine lymphoma.


Certain breeds of dogs have a higher than average risk of developing this disease and include Rottweilers, Scottish terriers, Golden retrievers but lymphoma can afflict any breed of dog.  Similarly, lymphoma can occur at any age, but the onset is generally in middle and older age.


Most of the time, lymphoma in dogs appears as “swollen glands” (lymph nodes) that can be seen or felt under the neck, in front of the shoulders, or behind the knee. Occasionally, lymphoma can affect lymph nodes that are not visible or palpable from outside the body, such as those inside the chest or in the abdomen. Other symptoms include vomiting, diarrhea, loss of appetite, weight loss, lethargy, difficulty breathing and increased thirst or urinations. Cutaneous lymphosarcoma can cause redness or flakiness of the skin, ulceration (especially near the lips and on the footpads), itchiness or lumps in the skin. Clinical signs will vary depending on the stage of the disease, volume of tumor and anatomic location of the lymphoma.