PLK1 and head and neck cancer: Based on our analysis, we found that CCND1/CDK4/PLK1/CD44 signatures were linked with shorter survival percentages in a group of multiple cancer types, including bladder carcinoma, breast cancer, colon adenocarcinoma, glioblastoma multiforme, head and neck cancers, leukemia, NSCLC, and ovarian cancer (Figure 3).