The colon is a part of the digestive tract whose primary function is the absorption of water and nutrients from food. Colon cancer is a leading cause of mortality worldwide.
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Recent evidence suggests that microbiota alternations in the gut are directly associated with colon cancer - it is found that oral bacterium leads to the progression of cancer cells in the colon. Precancerous cells or early undetected cancer cells facilitate the growth and progression of oral bacteria.
What are the causes of colon cancer?
Colon cancer is caused by genetic mutations, which lead to the formation of polyps. Polyps are precancerous cells, and polyp’s formation is the first stage of development of colon cancer.
Initially, colon cancers start with benign (noncancerous) lumps, which are known as adenomatous polyps. Genetic mutations develop up over some time - polyps may take around 20 years to develop into cancerous cells. However, external factors such as gut microbiota play a pivotal role in the progression of colon cancer and make it more aggressive.
The micro-organisms present in the human digestive tract play a significant role in digestion and metabolism. But dysbiosis in mouth microbiota may trigger the formation of tumor cells and enhance the progression of cancer cells.
The most common oral bacterium associated with colon cancer is Fusobacterium nucleatum (F. nucleatum), which accumulates with tooth decay. F. nucleatum is an anaerobic, gram-negative bacterium that is present in the digestive tract. The stable temperature and pH of the oral cavity promotes the growth of F. nucleatum, which accumulates in the periodontal plaque.
A comparison of healthy individuals and patients with colon cancer showed that colon cancer patients have abundant F. nucleatum (oral bacterium) compared to healthy individuals. The presence of F. nucleatum in the gut promotes the growth of cancerous cells in the colon; however, these bacteria do not affect noncancerous cells.
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What are the signs and symptoms of colon cancer?
The most common symptom of colon cancer is abdominal distension without any weight gain. Abdominal pain is infrequent in the case of colon cancer. Frequency of bowel movements changes along with some weight loss. Vomiting and nausea of unknown cause are also common during colon cancer.
How do oral bacteria cause colon cancer?
F. nucleatum is present in the oral cavity, but it can enter the bloodstream. Through the bloodstream, it enters the colon and other parts of the digestive tract. F. nucleatum produces a molecule termed FadA adhesin, which turns on several genes in the colon and results in the formation of cancerous cells in the colon.
FadA adhesin protein speeds up the formation and growth of cancerous cells in the colon. FadA adhesin protein has its effect only on cancerous cells. They do not affect the healthy cells in the colon. The probable reason for this is that healthy cells do not produce the proteins in response to FadA adhesion.
F. nucleatum leads to the growth of cancer cells only in the case of a few individuals, and they do not affect all individuals. This is due to the different community nature of oral bacteria and the multifactorial etiology of cancer cells.
Management of oral bacterium in colon cancer
A significant reduction in the number of F. nucleatum can enhance the recovery process in patients with colon cancer. Hence, improved oral hygiene plays a crucial role in limiting the growth and spread of cancerous cells.
A scientific approach to getting rid of colon cancer progression is through targeting the signaling pathway of oral bacteria. Disruption of the signaling path or suppression of FadA adhesin protein synthesis can significantly delay the speedy growth and spread of cancerous cells.
Another approach to manage colon cancer is the use of probiotics. Administration of probiotics or prebiotics significantly reduces the composition and number of F. nucleatum. This also helps in controlling the progression of cancerous cells in the colon.
Antibiotics, along with other antitumor drugs, are also given to patients with colon cancer. Antibiotics have shown promising results in the management of colon cancer by destroying the F. nucleatum.
- Whitmore, S.E., et al. (2014).Oral bacteria and cancer. PLoS pathogens,10(3).
- Sun, C.H., et al. (2019). The role of Fusobacterium nucleatum in colorectal cancer: from carcinogenesis to clinical management. Chronic Diseases and Translational Medicine, 1;5(3):178-87.
- Flemer, B., et al. (2018). The oral microbiota in colorectal cancer is distinctive and predictive. Gut, 1; 67(8):1454-63.