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The Fusobacterium nucleatum has been suggested by a new study to be connected with metastasized colon cancer.A joint study found evidence that the bacterium thrives in the liver, where colon cancer cells have metastasized.The study was performed by the researchers from Harvard Medical School, Massachusetts Institute of Technology, Vall d'Hebron University Hospital, Harvard T.H.Chan School of Public Health, and Yale School of Medicine.
"Colorectal cancers comprise a complex mixture of malignant cells, non-transformed cells, and microorganisms. Fusobacterium nucleatum is among the most prevalent bacterial species in colorectal cancer tissues," researchers noted.
The existence of bacteria where cancer cells grow has been reported in previous research.Researchers wondered if these strains of bacteria actually contribute to the formation of tumors.Experts call them carcinogenic bacteria known or suspected to cause cancer cell growth.
- Salmonella typhi is a bacterium that causes systemic infections and typhoid fever.It has been associated with gallbladder cancer, according to a study in 2015.
- Streptococcus bovis is bacterium associated with endocarditis, the inflammation of the heart's lining.It has been associated with colorectal cancer, according to studies in 2004 and 2006.
- Chlamydia pneumoniae is a bacterium that causes pneumonia.It has been associated with lung cancer, according to a study in 2003.
- Mycoplasma is a genus of bacteria unaffected by common antibiotics, such as penicillin, due to the lack of cell wall.The several species of the bacteria are pathogenic agents in humans.Diseases caused by the Mycoplasma genus include pneumonia and respiratory disorders, pelvic inflammatory diseases, and bacterial vaginosis.Several Mycoplasma species have been found in different cancer types, according to studies in 1995, 2001, and 2012.
- Helicobacter pylori is a bacterium usually in the stomach.It is often found in people with chronic gastritis and gastric ulcers.It has been associated with stomach cancer and mucosa-associated lymphoid tissue or MALT lymphoma, according to a study in 2006.
In the recent study, the researchers collected samples from actual patients with tumors present in their colon and liver.They found that the Fusobacterium nucleatum was present in colon tumors and the metastasized tumors in the liver.They also found that some patients who had colon tumors without the bacteria present, also did not have liver tumors with the bacteria.
To determine the connection between the bacteria and cancer cells, the researchers implanted tumors from the patients into healthy rat models.Their findings revealed the following:
- Tumors without the presence of the bacteria failed to gain complete control.But tumors with the bacteria grew.
- Use of an antibiotic to destroy the bacteria slowed down the growth of tumors.
- Bacteria have been suggested to travel with tumor cells and remain in new sites invaded by abnormal cells.
The researchers plan to investigate the possible involvement of bacteria in the tumor development in future studies.
Role of Bacteria in Cancer Growth
The theory of bacteria's involvement in cancer growth can be traced back to the 19th century with Dr.William Bradley Corey, the Father of Cancer Immunology.Dr.Corey's theory was about the causes of cancer and the role of microbes to promote the growth of abnormal cells.But the theory had suffered a setback, the difficulty of finding causal links between bacterial infections and human cancers.
The truth from Dr.Corey's theory came to light, after Barry Marshall and Robin Warren unveiled their findings in 1982.Their study revealed that H.pylori bacterium is a causative agent on most gastric ulcer cases.Today, some studies have noted additional factors in bacteria and cancer association, such as from Dr.Michael Karin, a professor of molecular biology at the UC San Diego School of Medicine.Dr.Karin suggested the effect of inflammation on cancer development.
"Inflammation is believed to account for about 20 percent of all cancers but it probably plays a role in more than 80 to 90 percent of all cancers," said Dr.Karin.
When tissues are damaged by infection or trauma, inflammation occurs to signal immune response to kill pathogens.Inflammation also signals nearby cells to repair the damaged tissues.But chronic inflammation that lasts for years can be associated with cancer development, according to a study in 2010.
The 2010 study suggested the role of inflammation in different stages of cancer development, such as initiation, promotion, invasion, and even metastasis.The study also suggested that only a minority of cancers was caused by germline mutations, mutations in egg or sperm cells.Meanwhile, 90 percent were attributed to environmental factors and somatic mutations, mutations of all other cells except the egg and sperm cells.Cancers associated with environmental factors were linked to chronic inflammation.About 20 percent of cancers were related to chronic infections, 30 percent may be associated with direct contact to pollutants, such as exposure to asbestos or cigarette smoking, and 35 percent may be attributed to dietary factors.
In a study by Dr.Rudolf Virchow, bacteria-induced chronic inflammation can result in the production of certain molecules that damage DNA.Damaged DNA in cells leads to mutations and eventually cancer development.