PLK1 and cancer: The analysis showed the amplification of CCND1/CDK4/PLK1/CD44 based on percentages of separate genes, with 7% for CCND1, 2.9% for CDK4, 1.7% for PLK1, and 1.8% for CD44 in multiple cancers, including the missense mutation amplifications, deep deletions, and alteration frequencies of these oncogenes.