CCL2 and head and neck squamous cell carcinoma: HNC: head and neck cancer; OSCC: oral squamous cell carcinoma; RT-PCR: reverse transcription polymerase chain reaction; ELISA: enzyme-linked immunosorbent assay; IL: interleukin; EGF: epidermal growth factor; GROα: growth-regulated protein alpha; TNF-α: tumor necrosis factor-alpha; VEGF: vascular endothelial growth factor; MCP-1: monocyte chemoattractant protein-1; HNSCC: head and neck squamous cell carcinoma.