Recent studies have also reported that Porphyromonas gingivalis promotes OC development and progression by stimulating oral squamous cell carcinoma proliferation and inducing the expression of key molecules nuclear factor kappa B (NF-κB), interkeukin-6 (IL-6) signal transducer and activator of transcription 3 (STAT3), cyclin D1, matrix metallopeptidase 9 (MMP-9), and the bacterial gingipains which are implicated in tumorigenesis. Here, MMP9 is linked to oral cavity squamous cell carcinoma.