Intestinal flora and tumors: a game in the microscopic world

Author: Wang Yu, attending physician of Changzhi People's Hospital

Reviewer: Zhao Jun, Chief Physician, Changzhi People's Hospital

1. Intestinal flora: the body’s internal guardian

In our bodies, there is such a huge "microbial kingdom", among which intestinal flora is the main combat force of this kingdom. They are not only an important part of the digestive system, but also a loyal guard to maintain our health. Imagine that your intestines are like a castle, and these bacteria are the soldiers stationed here, guarding this fortress day and night.

Figure 1 Original copyright image, no permission to reprint

The intestinal flora is mainly composed of three categories: beneficial bacteria, neutral bacteria and harmful bacteria. Beneficial bacteria, such as lactic acid bacteria and bifidobacteria, produce short-chain fatty acids (SCFAs) by fermenting food residues, provide energy for intestinal cells, and help maintain intestinal barrier function. Neutral bacteria are usually in a balanced state, neither bringing obvious benefits nor causing harm. However, when harmful bacteria dominate, problems arise - they may cause inflammation, damage the intestinal barrier and even promote the occurrence of diseases.

Figure 2 Original copyright image, no permission to reprint

In order to better understand the role of intestinal flora, scientists have likened it to a "second genome". Studies have shown that the number of intestinal flora can reach 1014, which is more than ten times the number of cells in the human body! They are involved in many physiological processes from nutrient absorption, immune regulation to mental health. It can be said that without this group of invisible allies, our health will become vulnerable.

2. Intestinal flora and the occurrence and development of tumors

When the ecological balance of intestinal flora is broken, they will become accomplices of disease. This imbalance phenomenon is called "intestinal flora imbalance". Recent studies have found that intestinal flora imbalance is closely related to the occurrence of various cancers, including colorectal cancer, gastric cancer, and breast cancer. So what mechanisms do intestinal flora promote the occurrence and development of tumors?

First, certain harmful bacteria can directly or indirectly promote the development of tumors. For example, enterotoxigenic Escherichia coli can damage DNA by secreting toxins, thereby increasing the risk of cancer. In addition, Helicobacter pylori infection has been listed as a Class I carcinogen by the World Health Organization. It can cause chronic gastritis, which in turn leads to abnormal proliferation of gastric mucosal cells.

Secondly, intestinal flora imbalance can also change the local microenvironment, thereby promoting tumor growth. For example, metabolites produced by certain bacteria (such as secondary bile acids) have pro-inflammatory effects, and long-term exposure to these substances may lead to persistent inflammatory responses, and inflammation is the breeding ground for many tumors.

Even more surprising is that the intestinal flora can also affect human health through the "gut-liver axis" or "gut-brain axis". For example, certain bacteria in the intestine can activate the immune system and release pro-inflammatory factors into the blood circulation, eventually reaching the liver or other tissues, thereby inducing a systemic inflammatory response. This mechanism may be the basis for the connection between non-intestinal tumors (such as pancreatic cancer or lung cancer) and the intestinal flora.

Therefore, maintaining a balanced intestinal flora is not only related to the health of the digestive system, but may also directly affect our ability to prevent cancer.

3. Effect of intestinal flora on tumor treatment

With the development of precision medicine, people have gradually realized the important role of intestinal flora in tumor treatment. Whether it is traditional chemotherapy drugs or emerging immunotherapy, their efficacy may be affected by intestinal flora.

Take immune checkpoint inhibitors (ICIs) as an example. This type of drug enhances the anti-tumor effect by relieving the tumor's inhibitory effect on the immune system. However, the efficacy of immunotherapy varies significantly among different patients, and a key factor behind this is the composition of the intestinal flora. Studies have found that patients with specific beneficial bacteria tend to show higher sensitivity to ICIs. On the contrary, if there are too many harmful bacteria in the intestines, it may weaken the effect of immunotherapy.

Similarly, in the field of chemotherapy, intestinal flora also plays an important role. For example, certain bacteria can metabolize chemotherapy drugs, thereby affecting their drug activity and toxicity. A study on mice showed that mice lacking intestinal flora had significantly reduced anti-tumor effects after receiving oxaliplatin treatment. This suggests that optimizing the patient's intestinal flora status may be a new strategy to improve the effectiveness of chemotherapy.

In addition, fecal microbiota transplantation, as an emerging therapy, is gradually being applied in clinical practice. By transplanting the intestinal flora of healthy donors to patients, it can not only restore the balance of their intestinal flora, but also improve the overall efficacy of tumor treatment.

IV. Looking to the future: from basic research to clinical application

Although significant progress has been made in the study of the relationship between intestinal flora and tumors, there are still many unknown areas waiting for us to explore. For example, which specific bacterial species or metabolites really determine the occurrence and development of tumors? How to design individualized intervention plans? The answers to these questions will reveal more potential tumor treatment targets for us.

We still have a long way to go from basic research to clinical application. Currently, scientists are working to develop diagnostic tools and treatments based on intestinal flora. For example, using metagenomics technology to analyze the characteristics of a patient's intestinal flora can achieve early tumor screening; and through probiotic supplements or dietary adjustments, it is expected to improve the patient's prognosis.

It is worth noting that lifestyle choices also largely determine the state of the intestinal flora. A high-fiber diet, regular work and rest, and moderate exercise have all been shown to be beneficial for maintaining the diversity of intestinal flora. Therefore, in addition to relying on modern medical means, each of us can protect our own "inner city guards" through daily behavior.

With the advancement of science and technology, I believe we will eventually unlock the complex code between intestinal flora and tumors. The arrival of this day will completely change the way we fight cancer.

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