In non-Hodgkin's lymphoma (NHL), either abnormal cells in the lymphatic system divide and grow without order or control or old cells do not die normally. Lymphatic tissue is present in many areas of the body, so non-Hodgkin's lymphoma can start almost anywhere in the body.

Non-Hodgkin's lymphoma may occur in a single lymph node, a group of lymph nodes, or an organ, and it can spread to almost any part of the body, including the liver, bone marrow, and spleen. Health professionals classify NHL into stages based on where the lymphoma is growing in the body.

Over time, lymphoma cells replace the normal cells in the bone marrow. This causes bleeding problems and infections. As the lymphoma cells spread, the body becomes less and less able to produce blood cells that carry oxygen to other tissues and to protect itself from infection.

Long-term survival depends on the type of non-Hodgkin's lymphoma and the stage of the disease when it is diagnosed. Approximately 75% of people diagnosed with non-Hodgkin's lymphoma are alive 1 year after the disease is diagnosed. That number drops to about 60% at 5 years and 40% at 10 years.²