BCL2 and cancer: For example, miR-15 and miR-16 target mRNA of the anti-apoptotic BCL2 gene, which plays a key role in several human cancers including leukemia, lymphoma and carcinoma. 22-24  The first evidence of miRs involvement in cancer was demonstration of down-regulation or deletion of miR-15a and miR-16-1 in most patients with CLL.   25  Aberrant regulation of miRs is mediated by several mechanisms including deletion, gene amplification, mutation or regulation of transcription factors that target a specific miR.