Oral Microbiota-A New Frontier in the Pathogenesis and Management of Head and Neck Cancers

Abstract

Head and neck squamous cell carcinoma (HNSCC) comprises the majority of tumors in head and neck tissues. The prognosis of HNSCC has not significantly improved for decades, signifying the need for new diagnostic and therapeutic targets. Recent evidence suggests that oral microbiota is associated with carcinogenesis. Thus, we conducted a comprehensive systematic review to evaluate the current evidence regarding the role of oral microbiota in HNSCC and whether their targeting may confer diagnostic, prognostic or therapeutic utility. Following the screening of 233 publications retrieved from multiple databases, 34 eligible studies comprising 2469 patients were compiled and critically appraised. Importantly, many oral pathogens, such as Porphyromonas gingivalis and Fusobacterium nucleatum were linked to certain oral potentially malignant lesions and various types of HNSCC. Furthermore, we summarized the association between the expression profiles of different oral bacterial species and their tumorigenic and prognostic effects in cancer patients. We also discussed the current limitations of this newly emerging area and the potential microbiota-related strategies for preventing and treating HNSCC. Whilst many clinical studies are underway to unravel the role of oral microbiota in cancer, the limited available data and experimental approaches reflect the newness of this promising yet challenging field.

Keywords: DNA/RNA sequencing; biomarker; cancer; head and neck squamous cell carcinoma; metastasis; microbiome; prognosis; treatment.

Figure 1

PRISMA flowchart of the study selection process.

Figure 2

The different methods used for collecting and characterizing oral microbiota from patients with head and neck squamous cell carcinoma. (A) Oral microbiota samples are obtained by means of saliva expectoration; mouth wash samples; oral swab samples; or tissue biopsy. (B) Oral microbiota were characterized by DNA-DNA hybridization; primers targeting the 16S ribosomal RNA gene. (C) Immunohistochemistry of tumor sections was also used to identify oral microbiota.

Figure 3

The relative abundance of the studied oral microbiota in oral squamous cell carcinoma (OSCC). (A) The bacterial species shown to have a higher abundance in OSCC (red circles; red arrow). (B) The bacterial species shown to have a lower abundance in OSCC (green circles; green arrow). In addition, a few species were shown to be increased in some studies and decreased in others (orange circles; orange double-headed arrow).