- Cancer remains a serious worldwide health concern even after decades of research. The part that microorganisms play in the onset and spread of cancer has come under closer examination recently. This review's main objective is to highlight the important relationships between various cancers and the bacteria in the human mouth. Many oral bacteria (such as Fusobacterium nucleatum, Porphyromonas gingivalis, and Streptococcus sp.), some viruses (such as human papillomavirus, Kaposi sarcoma Herpesvirus (KSHV), Human herpesvirus 1, and Epstein-Barr virus (EBV)), members have also been linked to lung, pancreatic, stomach, esophageal, and colon/rectum malignancies. Additionally, the current research describes several carcinogenic pathways that underlie the reported microbial links with cancer. In the oral cavity, there are about 700 different types of bacteria. Saliva and the various oral cavity habitats influence the population of the oral microbiome. The composition of the oral microbiome may change if certain risk factors for oral cancer such as alcohol, tobacco, and betel nuts are used. In oral cancer, commensal and pathogenic bacteria have played a major role. Bacterial products and their metabolic byproducts have the potential to permanently modify the host's epithelial cells' DNA, promoting their survival and/or proliferation. Fusobacterium nucleatum and Porphyromonas gingivalis alter the host cell's DNA, which supports the production of inflammatory cytokines, proliferation of cells, and the suppression of apoptosis, cellular invasion, and migration. In this review, we discuss how the microbiome functions as a predictive and early diagnostic biomarker for oral cancer and its involvement in the course of the disease.

Index Terms- Oral squamous cell carcinoma (OSCC), Head-and-neck squamous cell carcinoma (HNSCC), Oropharyngeal squamous cell carcinoma (OPSCC), Porphyromonas gingivalis (P. gingivalis).