Lymphoma is cancer that begins in the lymph system in white blood cells called lymphocytes. When these cells become abnormal, they don't protect the body from infection or disease. They also grow without control and may form lumps of tissue called tumors. Or it can spread to almost any part of the body, including the liver and bone marrow. Sometimes they are grouped as: Slow-growing lymphomas, which spread slowly and cause few symptoms. Fast-growing lymphomas, which spread quickly and cause severe symptoms. These may also be called aggressive lymphomas and may be classified as intermediate-grade or high-grade. Treatment can cure some people and may allow others to live for years.