The Microbiome of Tumors & Carcinogens

Recent research has revealed that the tumor microenvironment is not only shaped by cancer cells, but also by a diverse community of microbes that can influence carcinogenics. From altering immune responses to affecting how cancer develops and responds to treatment, the tumor-associated microbiome plays a crucial role in health and disease.

Understanding these interactions is key to unlocking innovative strategies in cancer therapy, which is why we put together this research guide.

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What is the Tumor Microbiome?

The tumor microbiome or tumor microenvironment (TME) refers to the ecosystem of microorganisms within tumors and their surrounding microenvironment. Key elements of the tumor microbiome include malignant cells and non-malignant components, including immune cells, elements of the extracellular matrix, stromal cells, and endothelial cells.

How Does the Microbiome Affect Tumors?

Evidence suggests that the tumor microbiome plays a significant role in tumor progression and cancer cell survival. Microbes within the tumor microenvironment can influence cancer cell behavior by modulating cellular proliferation, apoptosis, and metastasis. The tumor microbiome also impacts immune evasion, where microbial components may suppress immune responses, allowing tumors to grow unchecked.

As chronic inflammation driven by microbial dysbiosis can also potentially promote carcinogenesis and microbiome composition can impact how tumors respond to cancer therapies such as immunotherapy, chemotherapy, and radiotherapy, early microbiome interventions could be the key to better therapeutic responses and more targeted and effective cancer treatments.

What is Carcinogenicity?

Carcinogenicity refers to the capability of a substance or exposure to cause cancer. Scientists evaluate the carcinogenicity of substances through laboratory studies, animal testing, and epidemiological research in humans. Carcinogens are the substances or exposures that are known to increase the risk of cancer, with commonly known examples including tobacco smoke, asbestos and ultraviolet (UV) radiation.

How the tumor microbiome affects carcinogenicity

In addition to these common external carcinogenic exposures, some microbial pathogens (such as certain bacteria, viruses, and parasites) are also classified as carcinogenic because they can contribute to cancer development. 

This is where the microbiome comes into play, as these microorganisms can influence carcinogenic processes in several ways:

• Metabolic transformation: Some gut bacteria can metabolize dietary components into compounds that may be carcinogenic or, conversely, into substances that protect against cancer.
• Immune modulation and inflammation: The microbiome plays a crucial role in regulating the immune system and inflammation. An imbalance (known as dysbiosis) can lead to chronic inflammation, which has been linked to the development of cancers such as colorectal cancer.
• Interaction with carcinogens: The microbiome may alter how the body processes environmental carcinogens, potentially influencing an individual’s overall risk of cancer.

Different Types of Carcinogenic Microbes

The International Agency for Research on Cancer (IARC) has identified 10 pathogens classified as directly carcinogenic to humans. These pathogens include bacteria, viruses, and parasites, as follows:

• One bacterium: Helicobacter pylori
• Six viruses: hepatitis B virus (HBV), hepatitis C virus (HCV), human papillomavirus (HPV; types 16, 18, 6, 11, 31, 33, 45, 52, 58, and other HPV types), Epstein–Barr virus (EBV), human herpesvirus type 8 (HHV-8; also known as Kaposi sarcoma-associated herpesvirus), and human T-cell lymphotropic virus type 1 (HTLV-1)
• Three parasites: Opisthorchis viverrini, Clonorchis sinensis and Schistosoma haematobium

Below is a more detailed breakdown and comparison of these carcinogenic microbes.

HIV & Carcinogenic Enhancement

In addition to the 10 carcinogenic pathogens identified above, while HIV itself is not directly carcinogenic, it is noted by the IARC to play a significant role in enhancing the carcinogenic action of other pathogens. HIV-induced immunosuppression allows co-infections, such as HHV-8, HPV, and EBV, to drive cancer development. For instance:

• Kaposi sarcoma: Caused by HHV-8 in HIV-positive individuals.
• Cervical and anal cancer: Driven by HPV in immunosuppressed patients.
• Lymphomas: Linked to EBV in HIV-positive individuals.

By excluding HIV from direct classification, the IARC avoids double-counting cancers attributable to co-infections.

Closing Thoughts

Ready to explore the molecular interplay between the tumor microbiome and carcinogenic exposures? Discover how our cutting-edge immuno-oncology sequencing services can provide comprehensive insights into your tumor samples, helping you identify key microbial and carcinogenic factors that influence health and disease.

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Tumor Microbiome & Carcinogenicity FAQs

What cancers are related to the microbiome?

Tumor associated microbiota are linked to various cancers including ovarian cancer, endometrial cancer, prostate cancer, small cell lung cancer, and non small cell lung cancer, highlighting the potential role of the microbiome in cancer development, diagnostics and treatment.

What is the interaction between the microbiome and tumors?

The microbiome interacts with tumors by altering the tumor microenvironment through immune modulation and metabolic changes, as seen in tumor samples from ovarian cancer patients and lung cancer patients, which can influence cancer progression and overall health and disease.

What bacteria is associated with tumors?

Research shows fusobacterium nucleatum (f nucleatum) is a notable bacterium associated with tumors, having been detected in samples from within the tumor microenvironment in breast and pancreatic tumors.

What cancers are caused by bacteria?

Helicobacter pylori is a bacteria that has been identified as a carcinogenic pathogen by the IARC, causing inflammation and DNA damage, and creating a favorable environment for carcinogenesis that may facilitate the progression from chronic gastritis to gastric cancer.

Why do tumors get infected?

Tumors may get infected due to disruptions in local immune defenses and the altered microenvironment, allowing tumor associated microbiota to colonize and become infected.