Lymphoma is a general term for cancers that develop in the lymphatic system. One type is called Hodgkin's. All other lymphomas are grouped together and are called Non-Hodgkin's lymphoma.

The lymphatic system is part of the body's immune defence system. Its job is to help fight diseases and infection. The lymphatic system includes a network of thin tubes that branch, like blood vessels, into tissues throughout the body. Lymphatic vessels carry lymph, a colourless, watery fluid that contains infection-fighting cells called lymphocytes.

Along this network of vessels are small, bean-shaped organs called lymph nodes. Clusters of lymph nodes are found in the underarms, groin, neck, chest and abdomen. Other parts of the lymphatic system include the spleen, thymus, tonsils and bone marrow.

With lymphoma, these cells in the lymphatic system grow abnormally. They divide too rapidly and grow without any order or control. Too much tissue is formed, and tumours begin to grow. The cancer cells can also spread to other organs.