Lymphoma cancer cell. Coloured scanning electron micrograph (SEM) of a lymphoma cell showing early apoptotic changes. A lymphoma is a cell of the immune system that has become cancerous. The cell becomes immortal and can grow indefinitely. A number of these cells will form a tumour. Lymphomas most commonly occur in the lymph nodes and spleen, which are rich in tissue containing lymphocytes, and can spread to the liver and bone marrow. Lymphoma cancers are classified into either Hodgkin's lymphoma (presence of Reed-Sternberg cells) or non- Hodgkin's lymphoma. Treatment is with chemotherapy and radiation therapy and is often successful. Programmed cell death or apoptosis occurs when a cell becomes old or damaged. Magnification: x9000 when printed at 10 centimetres wide