Abstract
Nowadays cancer is the second main cause of death in the world. The most known bacterial carcinogen is Helicobacter pylori. Pathogens that can have an impact on cancer development in the gastrointestinal tract are also found in the oral cavity. Some specific species have been identified that correlate strongly with oral cancer, such as Streptococcus sp., Peptostreptococcus sp., Prevotella sp., Fusobacterium sp., Porphyromonas gingivalis, and Capnocytophaga gingivalis. Many works have also shown that the oral periopathogens Fusobacterium nucleatum and Porphyromonas gingivalis play an important role in the development of colorectal and pancreatic cancer. Three mechanisms of action have been suggested in regard to the role of oral microbiota in the pathogenesis of cancer. The first is bacterial stimulation of chronic inflammation. Inflammatory mediators produced in this process cause or facilitate cell proliferation, mutagenesis, oncogene activation, and angiogenesis. The second mechanism attributed to bacteria that may influence the pathogenesis of cancers by affecting cell proliferation is the activation of NF-κB and inhibition of cellular apoptosis. In the third mechanism, bacteria produce some substances that act in a carcinogenic manner. This review presents potentially oncogenic oral bacteria and possible mechanisms of their action on the carcinogenesis of human cells.
Highlights
Nowadays cancer is the second main cause of death in the world
The high salivary counts of studied bacteria may be diagnostic indicators of oral squamous cell carcinoma P. gingivalis was abundantly present in malignant oral epithelium Bacteria were the most common isolates from cervical lymph nodes in patients with oral cancer Head and neck squamous cell carcinoma (HNSCC) saliva samples were associated with increased amounts of Streptococcus and Lactobacillus and a decrease in Haemophilus, Neisseria, Gemella, and Aggregatibacter S. anginosus infection is implicated in the carcinogenesis of HNSCC
P. gingivalis is a biomarker for microbe-associated risk of death due to orodigestive cancer Studied bacteria could have a significant role in the carcinogenic process by causing inflammation and by promoting the carcinogenesis The abundance of P. gingivalis is trended with higher risk of esophageal squamous cell carcinoma, and T. forsythia is associated with higher risk of esophageal adenocarcinoma Increased carriage of presented bacteria was found in patients with Colorectal cancer (CRC); lower abundance of Clostridium sp. was simultaneously observed Fusobacterium enrichment is associated with specific molecular subsets of colorectal cancers
Summary
Nowadays cancer is the second main cause of death in the world. It is estimated that in 2018 about 9.6 million people will have died from cancer. According to the World Health Organization (WHO), there are an estimated 657,000 new cases of cancers of the oral cavity and pharynx each year, and more than 330,000 deaths [3]. There are data suggesting the role of oral cavity bacteria in the development of cancer. Such bacteria can be responsible for oral cancers, as well as tumors of the gastrointestinal tract. Titles and abstracts of found papers were examined to order to determine which articles to exclude or include in the review. Ninety-eight articles were included in this narrative review. Potentially oncogenic oral bacteria are presented along with the possible mechanisms of their action on carcinogenesis of human cells
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