PLK1 and head and neck squamous cell carcinoma: In HNSCC from the TCGA cohort, high levels of Plk1 mRNA correlated with shorter disease-free survival (DFS, 19.05 months vs 46.81 months, p = 0.006, Figure 1C) and shorter overall survival (OS, 32.36 months vs 64.78, p = 0.0009, Figure 1D).