After the intestine, the mouth is the second largest reservoir of microbes. It harbors more than 700 species of bacteria that colonize teeth, tongue and soft tissues – which can be catalysts for cancer.
There is increasing evidence that the oral microbiome influences the risk of developing certain types of cancer and affects the prognosis of those who develop them.
A recent investigation into the JAMA Oncoloy analyzed data from three longitudinal studies in the USA, involving 159,840 participants, correlating the presence of up to 13 bacterial species in saliva with the subsequent development of squamous cell carcinoma of the head and neck.
The researchers also detected a moderate association with so-called orange and red complex bacteria, which have a strong link to gum disease. Together, the presence of these bacteria has been associated with a significant increase in the risk of head and neck cancer.
At the beginning of this year, another study, cited by , had already identified seven species associated with tumors of the oral cavity.
Although these studies highlight the role of bacteria in the development of cancer, particularly in the early stages, there is a lack of definitive evidence to establish a direct causal relationship between bacteria and cancer.
The bacteria Fusobacterium nucleatumfor example, has been studied for its ability to protect cancer cells from immune attacks. One, done at Hadassah-Hebrew University in Jerusalem, and his colleagues, revealed that this species helped protect cancer cells from immune attack.
This could give tumors almost free rein to grow, the Portuguese scientist told New Scientist Miguel Reis Ferreira from King’s College London, who is investigating the role of microbes in improving cancer treatment.
A recent investigation by Reis Ferreira’s own research group found that people with head and neck cancer who have higher levels of F. nucleatum in fact, they have a better prognosis than those with lower levels.
Follow-up laboratory experiments also identified a large reduction in the number of cancer cells viable after having been infected with the bacteria F. nucleatum: “Essentially, they melt the cancer cells in the head and neck.”
Referring to the research published in September (described in the third paragraph), the Portuguese scientist says that it does not prove that those bacteria cause cancer. “It could just be an association, because these bacteria develop in environments where there is a lot of inflammation, and the Inflammation is, in itself, a known risk factor for cancer“.
