Mantle Cell Lymphoma (MCL) is a cancer of white blood cells, which help to fight infections. The B lymphocyte is located in the outer edge of a lymph node follicle (the mantle zone). The transformed B lymphocyte grows in an uncontrolled way, resulting in the accumulation of lymphoma cells, which causes enlargement of lymph nodes. Sometimes, when these lymph nodes become very large, or grow in other parts of the body, they can be called “tumors.” The MCL cells can enter the lymphatic channels and the blood, and can spread to other lymph nodes or tissues, such as the marrow, liver and gastrointestinal tract. MCL occurs more frequently in older adults – the average age at diagnosis is the mid-60’s.