Mantle cell lymphoma (MCL) is a rare, B-cell NHL that most often affects men over the age of 60. The disease may be aggressive (fast growing) but it can also behave in a more indolent (slow growing) fashion in some patients. MCL comprises about five percent of all NHLs. The disease is called "mantle cell lymphoma" because the tumor cells originally come from the "mantle zone" of the lymph node. MCL is usually diagnosed as a late-stage disease that has typically spread to the gastrointestinal tract and bone marrow.