CCND1 and mantle cell lymphoma: MCL patients with downregulated miR-34a had short overall survival associated with poor prognosis. Low expression of miR-34a was associated with high expression of MYC oncogene, which was co-regulated with CDK4/6 and CCND1 to further promote cell-cycle progression and the development of MCL.MiR-34a is involved in the regulation of the tumor suppressor gene TP53 via FOXP1 and BCL2, thus affecting the differentiation and apoptosis of B cells.