Molecular mechanisms of BCL2 overexpression in MCL are complex and comprise BCL2 genomic gains (24%) and BCL2 mRNA overexpression as a result of aberrant activation of prosurvival pathways (e.g., nuclear factor kappa B (NFκB)) or as a result of loss of its negative regulators (e.g., loss of micro RNA miR-15/16 as a result of frequent 13q deletions). This evidence concerns the gene BCL2 and mantle cell lymphoma.