A New Horizon in Cancer Treatment and Research: Metagenomics! How Do Microorganisms Such as Bacteria and Viruses Cause Cancer?

Cancer is a major health problem in developed and developing countries, caused by combined genetic, environmental and lifestyle factors. Pollution, inadequately sterilized products and sometimes poor personal care increase interactions with bacteria and viruses, inviting different cancers. Microorganism-related cancers account for %16,1 of diagnosed cases worldwide.

Many beneficial bacterial species normally inhabit a healthy human body. However, disease-causing bacteria and/or viruses entering the body through contamination (interaction) are either recognized by the body's own immune system or killed through medical interventions. Environmental factors that weaken immunity, such as stress, dietary habits, antibiotics, chemotherapeutic and other agents, cause an increase in pathogenic (disease-causing) microorganisms in the body.

An increase in microorganisms causes an increase in the amount of toxic (poisonous) substances produced by microorganisms, particularly bacteria, in the body and/or chronic (long-term) infection in the organ or tissue they inhabit. Increased toxic substances and chronic infection increase the formation of free radicals that damage DNA (genetic material) in the body. The resulting free radicals disrupt the mechanisms that repair DNA damage in healthy cells and lead to the accumulation of mutations (genetic changes) in cells. As mutations accumulate, cells multiply in an uncontrolled, damaged manner and form tumors.

How Do Viruses or Bacteria Cause Cancer?

After entering the body, viruses, which are microorganisms, can attack cells and randomly incorporate their genetic material into DNA in the cell nucleus, causing excessive production of oncogenes that contribute to tumor development. Alternatively, they can add these oncogenes to their own genetic makeup and spread rapidly through the body, promoting tumor formation. These genes, normally involved in cell proliferation when produced at normal levels, prevent tumor-suppressing genes from functioning after undergoing mutation. They allow cells that should die to evade death mechanisms and multiply uncontrollably, contributing to tumor formation as other microorganisms do. All these events provide sufficient evidence to explain how microorganisms cause cancer.

What Is Metagenomics?

Metagenomic studies investigate relationships between microorganisms and cancer development. Metagenomic studiesare analyses of the genetic material of microorganisms that may be present in samples such as biopsy tissue. Metagenomic studies allow relationships between cancer development and microorganisms to be examined. This development enables analysis of microbial diversity and identification of microorganism species in tissue samples from cancer patients. By revealing microbial genetic sequences in tissue samples, metagenomics has made it easier to understand which species and/or their close relatives cause particular cancer types. As shown in the table below, analyses have proven that specific microorganism species cause specific cancer types.

All these developments shed light for scientists continually seeking new approaches to cancer treatment. Using metagenomics, which enables understanding of cancer at the molecular level, to develop treatments directed at microorganism species identified in tissue samples will also offer new paths for treating the cancers they cause.