PLK1 and neoplasm: Moreover, the mRNA of several cell cycle regulatory genes, such as Cdc25b, Cyclin B1, Cyclin A2, Plk1, Cks1, Aurora B, and Topo 2 alpha were decreased in prostates of TRAMP/SPDEF OE mice (Figure 4C, right panel), a finding consistent with decreased cellular proliferation and decreased tumor sizes.