Definition:

Follicular lymphoma (FL) is generally an indolent B cell lymphoproliferative disorder of transformed follicular center B cells. FL is characterized by diffuse lymphoadenopathy, bone marrow involvement, splenomegaly, and less commonly other extranodal sites of involvement. The genetic hallmark of FL, the translocation t(14;18)(q32;q21), results in the constitutive overexpression of the bcl 2 protein, which impairs the normal germinal centre apoptotic programme. Inactivating mutations of MLL2 are found in >80% of FL and interfere with the ability of MLL2 to activate gene transcription through H3K4 methylation. Mutations of other histone modifiers (CREBBP, EZH2, MEF2B, and EP300) are found in ;33%, 27%, 15%, and 9% of FL, respectively.