Research into the causes of cancer has produced information on genetic mutations along with viral causes, but studies into potential cancer bacteria also point to certain bacterial origins of the disease. An example is the presence of Helicobacter pylori in the stomach, which is known to cause stomach ulcers, but appears to also increase the likelihood of stomach cancer developing. Scientists looking into the potential connections of bacteria and cancers find hints to the possible link when unexpected numbers of a certain bacteria turn up in cancerous tissue.
Viral causes of cancers are commonly known, and vaccines are even available for some. An example of a virus that can be tackled with a vaccine is human papillomavirus (HPV,) which is sexually transmitted and can cause cervical cancer later in life. The hepatitis C virus is also well-known as a cause of cirrhosis and cancer of the liver. Cancer bacteria, though, are part of a completely different group of organisms to the viruses, as bacteria are cells and viruses are merely strands of genetic material wrapped in protective proteins.
Genetic mutations are a significant field of interest in cancer research, where many types of tumors have been associated with specific mutations in the genes of the affected person. Many mechanisms by which the mutations affect the development of the cancers have also been made clear, but in the case of tumors caused, or potentially caused, by microbes like viruses and bacteria, these mechanisms are, as of 2012, still unknown. Sometimes the only reason a cancer bacteria is proposed is because researchers have noticed its presence in cancerous tissue, where it was not expected to be found.
For example, in 2011, researchers at the British Columbia Cancer Agency tested colon cancer tissue and found that a certain kind of bacteria, called Fusobacterium, was present in the cancer at levels much higher than elsewhere in the body, and that the bacteria were also more likely to occur in cancers that had spread. Although this does not prove that the bacteria caused the cancer in the first place, it provides a jumping off point for further investigations into the interaction between the bacteria and the cancer cells. Helicobacter pylori, which is associated with stomach cancer, is thought to help trigger the cancer through the constant irritation and turnover of cells of the original ulcers it causes. Another possible type of cancer bacteria through indirect, or even direct mechanisms, is Chlamydia trachomatis, a sexually transmitted disease that appears to work in conjunction with HPV to produce cervical cancer.