CDH1 and head and neck squamous cell carcinoma: This hypothesis is in conjunction with known F. nucleatum pro-carcinogenic features associated with bacterial invasion and inflammation (e.g., flagella assembly and bacterial chemotaxis) [24,25,27], metabolic pathways (e.g., homolactic fermentation) [26], production of DNA-damage compounds [44], and promoted cell proliferation (e.g., E-cadherin/β-catenin signaling via its FadA adhesin) [45], suggesting that enrichment of F. nucleatum in early stages of tumorigenesis is an independent risk factor in patients lacking major risk factors for HNSCC.