Cancers with a Bacterial Contributor

In light of the study showing that bacteria with a particular form of the protein DnaK can interfere with a cell’s response to DNA damage and the ability to repair such damage, I have been thinking about what kinds of cancers may have a bacterial cause or contribution. The one that the researchers studied to find the link between DnaK and bacterial infection and cancer was the high frequency of lymphoma in patients with HIV. Well, they actually studied a mouse model of that cancer connection. The scientists found that a common bacteria, called mycoplasma, that is present on most people was responsible for the increased cancer risk.

human_microbiota_microbiome — Figure. 1 Human microbiota (the microbes that live within and on humans) and human microbiome (the genomes of the human-associated microbes). View larger

There are multiple strains of mycoplasma, and they can live on different parts of the body and can cause infectious disease. For example, in the respiratory system, mycoplasma can cause pneumonia. However, a study with children indicated that the bacteria are present even in many children who have no symptoms. This asymptomatic presence of a pathogen is called “colonization.” Indeed, our bodies are full of microbes (Figure 1). Most are not harmful. Indeed, many microbes that live on or in us contribute to health, affect behavior and emotions, process foods and provide nutrients, and influence the effectiveness of medicine. Imbalances in them contribute to disease and diseases and medicines affect the composition of a person’s microbiota. However, there may be situations when nonharmful bacteria can become harmful.

Considering that HIV, an immunodeficiency disease, increases the risk of bacterial-associated cancers, another possibility for bacterial infection to increase the risk of cancer would be in patients taking immunosuppressive or immunomodulatory medications for autoimmune disease or to prevent transplant rejection or graft versus host disease. Another normal condition that causes natural immunosuppression is pregnancy. Does an altered response to normally nonharmful bacteria in pregnant women affect the risk of developing cancer?

In thinking about how bacteria could contribute to cancer, one factor is the chance of the tissue or cells being exposed to the bacteria. Tissues or cells that are part of an organ that is “open” to the environment would seem to be at a higher risk for a bacterial contribution to a cancer. Those tissues would include the skin, breast (opening through the nipple), urinary tract, genital tract, respiratory system, and gastrointestinal system, along with the mouth. Immune cells also encounter bacteria because a major function of immune cells is to eliminate bacteria. Immune cells are also present in all of the organs that are exposed to the environment.

With these two factors (immunosuppression and exposure to bacteria) in mind, I generated the list below. In each case, some of the cancers have a clear known cause that is related to a specific mutation, genetic risk factor, or an environmental cause. However, the other cancers in these tissues have an unknown cause. These could be the ones likely to have a bacterial contribution or related to errors in DNA that are naturally introduced as cells replicate. In either case, for bacteria with the cancer-associated form of DnaK, it would hard to know if bacterial colonization contributed to the cancer, because the research indicated that the infection did not need to persist. DnaK could trigger events that result in mutations in the DNA that could lead to cellular transformation into a cancerous cell.

List of Potential Cancers with a Bacterial Cause

Lymphoma associated with certain immunomodulatory or immunosuppressive agents used to treat autoimmune diseases
Lung cancers without a clear environmental cause, like smoking or exposure to asbestos
Some breast cancers
Uterine cancers
Cervical cancers not associated with human papilloma virus (HPV)
Bladder cancers
Gastrointestinal cancers
Oral cancers not associated with tobacco use

It will be tricky to use the information that asymptomatic bacterial colonizations contribute to cancer. Ideally, one would want to use this information to develop preventative measures or treatment strategies. However, any strategies that eliminate such bacteria could have unintended consequences that are worse than the increased chance of getting cancer. By eliminating these bacteria, the natural balance of “good” microbes and “bad” microbes could be altered, which can lead to more dangerous or symptomatic disease. Balancing the cost-benefit ratio in manipulating the microbiome is more challenging than assessing this ratio for other treatments, because we are still in the early phases of understanding the metaorganism that humans truly are and how these vast populations of microbes influence health, behavior, emotions, and disease.

Related Sites

A. Reid, S. Greene, FAQ: Human Microbiome, January 2014, The American Academy of Microbiology. https://www.asmscience.org/content/report/faq/faq.3 (accessed 17 December 2018)

Human Microbiome, Word Microbe Day (27 June 2018) http://worldmicrobiomeday.com/human-microbiome/ (accessed 17 December 2018).

R. Conniff, Microbes: The Trillions of Creatures Governing Your Health. Smithsonian Channel May 2013 (https://www.smithsonianmag.com/science-nature/microbes-the-trillions-of-creatures-governing-your-health-37413457/) (accessed 18 February 2020).

Human Microbiome Project, National Institutes of Health. https://commonfund.nih.gov/hmp (accessed 17 December 2017)

Cite as: N. R. Gough, Cancers with a possible bacterial contribution. BioSerendipity (18 December 2018) https://www.bioserendipity.com/cancers-with-a-possible-bacterial-contribution/

Cancers with a Possible Bacterial Contributor

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