CCND1 and brain cancer: Together with CCND1, which leads to the hyperphosphorylation of the tumor suppressor protein retinoblastoma (pRb) and to its dissociation of the E2 promoter-binding protein dimerization partners (E2F) from the pRb/E2F complex, CCNE1 is considered to be a key oncogene and is overexpressed in breast, liver, lung, and brain cancers [22, 23].