Lymphoma (which is also known as malignant lymphoma and lymphosarcoma) is the single most common cancer that affects cats.

Lymphoma is a solid tumour of a type of white blood cell (lymphocyte) that is involved in immune responses. In addition to being present in the blood, there are accumulations of lymphocytes present elsewhere in the body – either in discrete sites (lymph nodes or 'lymph glands'), or present within other tissues.

Because of the wide distribution of lymphocytes in the body, and the movement of these cells through the body, lymphoma (a malignant tumour of these cells) can occur at virtually any site, and also commonly occurs at multiple sites. Common sites to be affected include the lymph nodes (distributed throughout the body), the chest cavity, the intestinal tract, the nose, the kidneys and the nervous system.

Lymphoma in cats is often classified according to the site (tissues) that are affected - common terms used include:

  • Alimentary lymphoma - affecting the stomach and/or intestines);
  • Mediastinal lymphoma - affecting lymphoid tissue in the chest cavity;
  • Multicentric or nodal lymphoma - affecting multiple lymph nodes and possibly other sites in the body too;
  • Extranodal or miscellaneous lymphoma - these are cases of lymphoma that don't clearly fall into one of the other categories eg, lymphoma affecting the kidneys, nose, brain etc.

Clinical signs vary widely according to the tissues that are affected. Both infection with feline leukaemia virus (FeLV) and feline immunodeficiency virus (FIV) can be underlying or predisposing causes of lymphoma development.

Various treatment options are available for lymphoma including surgery, drug therapy and radiation therapy. The treatment choice will depend on the site and form of the tumour, and the availability of the treatment options. In many cats the response to therapy can be very good and long lasting. Although uncommon, some cases of lymphoma will go into complete and permanent remission and thus some cats can effectively be 'cured'.

Surgery and/or chemotherapy are the two most common treatment options used, but it is very difficult to predict which cats will respond well to therapy for lymphoma. It can be helpful, especially with chemotherapy, to use trial therapy as the initial response to chemotherapy (how well the tumour responds in the first few weeks) is often the best predictor of long-term response.