Could the bacteria in your mouth help us detect cancer? We are getting more evidence suggesting the answer is yes.
We often speak of tobacco, alcohol, and obesity as significant causative agents. Historically, infections with bacteria have not been considered a significant risk factor for cancer. Still, we know that the microbes can be opportunistic, infecting healthy tissues after cancer has already planted its roots. Now, we are learning about a causative relationship between bacteria and cancer.
Microbes and cancer: History
Let’s look at a bit of history before turning to current evidence of the relationship between microbes and cancer.
In 1772, researchers speculated about Mycobacterium tuberculosis as a cause of cancer. They observed that lung cancers commonly occurred in regions of pulmonary scarring, presumably from tuberculosis. Also, those with lung cancer appeared to have TB more frequently compared to the general population. Alas, the TB-cancer theory did not pan out.
Like many hypotheses attributing cancer to specific infectious agents, however, the tuberculosis-cancer theory did not stand the test of time. In 1890, the Scottish pathologist William Russell provided circumstantial evidence for bacteria as a cause for cancer.
In 1926, the Canadian Thomas Glover reported consistently isolating a specific bacterium from animals and humans’ cancer-containing tissues. Investigators disputed Glover’s claims, given his refusal to repeat his research for the Public Health Service critics. From the 1930s, we have had increasing amounts of evidence supporting the microbe: cancer link.
Microbes and cancer: Today
One example of the microbe: cancer relationship involves the bacterium Helicobacter pylori and its role in stomach cancer. H. pylori lives can live in our stomach or intestines and may indirectly cause cancer via chronic inflammation or act more directly. This microorganism is also linked with a particular type of lymphoma in the stomach. H. pylori is the first bacterium designated as a definite cause of cancer in humans by the International Agency for Research on Cancer.
Viruses and cancer
More recently, we have discovered the role viruses can play in causing cancer. Human papillomavirus can spread by way of anal, oral, or vaginal sex. While low-risk types of HPV appear to be unrelated to cancer (but can cause warts), high-risk varieties (especially HPV16 and HPV18) can cause various kinds of cancer.
Have you been sexually active? Virtually all of us are infected with HPV almost immediately after sexual initiation, with roughly half of the infections involving high-risk bacterium strains. Fortunately, the vast majority of HPV infections never cause cancer.
On occasion, our immune system does not control HPV; the virus persists for years and can cause mutations that can lead to genital warts or cancer. Fortunately, HPV vaccines can markedly reduce the risk of infection with disease-causing HPV types.
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