The present disclosure identifies a novel subtype of follicular lymphoma (FL) characterized by dysregulation of the cyclin/CDK/RB proliferative pathway. This subtype of FL is associated with increased malignancy and mortality, relative to FL which is not associated with cell cycle dysregulation. Accordingly, this disclosure presents novel methods to subtype FL and stratify patient risk by detection of biomarkers associated with RB inactivation. This disclosure further presents novel therapies for the treatment of FL subtyped by inactivation of RB.