PPL and head and neck squamous cell carcinoma: In summary, we applied WGCNA approach to construct a gene co-expression network and identified one significant module (blue module) and ten hub genes (TGM1, IVL, PI3, LCN2, KLK5, SLPI, KLK7, PPL, TGM3, LOR), which were suggested to play crucial roles in the lymph node metastasis of HNSCC patients.