CCND1 and mantle cell lymphoma: Cyclin D1 facilitates cell cycle progression from the G1 to the S phase through complex formation with Cyclin D kinases 4 and 6, which phosphorylate retinoblastoma 1.35 Cyclin D1 overexpression occurs in more than 90% of mantle cell lymphoma patients as a consequence of a t(11;14) (q13;q32) translocation of Cyclin D1 and the IgH heavy chain.36 This overexpression deregulates the cell cycle, leading to rapid progression from the G1 to the S phase and subsequent proliferation.