Bacteria can help spread cancer through the body, study says

Bacteria that live inside cancer cells are perhaps one of the key factors in the spread of cancer to other parts of the body. The clues that this is happening come from a study carried out by Chinese researchers with mice, in which the presence of microorganisms was essential for tumor cells to be able to travel through the animals’ blood vessels.

The data have just come out in the scientific journal Cell, one of the most important in the world. Coordinated by Shang Cai of the West Lake Biomedicine and Life Sciences Laboratory in the city of Hangzhou, the work looked at rodent breast tumors, but there is good reason to think the findings could hold for tumors in humans as well.

It so happens that the relationship between bacterial activity and cancer is becoming an increasingly important research topic in recent years. Data on the subject accumulate in the case of tumors that affect the large intestine, for example, when different types of cancer are in contact with the intestinal microbiota (the community of microorganisms that inhabit the digestive system and can either help in the absorption of nutrients and cause disease).

There is less data, however, on the role of microbes that live inside the tumors themselves, although there is already evidence that there could be a correlation between the presence of certain bacterial species and the severity or type of progression of some cancers.

To investigate this in detail, the Chinese team studied a type of breast tumor that naturally affects laboratory mice (several types of cancer, by the way, are relatively common in rodents). In their analyses, they took advantage of the fact that some antibiotics only act on bacteria that are circulating in the bloodstream, while others are able to kill the microorganisms that colonize the interior of cells (the so-called cytoplasm). Thus, by selectively eliminating the “external” bacteria, it was possible to investigate the effects of those that inhabit the interior of tumor cells.

Using this approach, they found that the presence of bacteria inside or outside tumor cells has no effect on tumor growth, but appears to have a considerable impact on the emergence of so-called metastases, that is, the emergence of new foci of cancer in organs distant from where the disease originally appeared.

In an interview with Sheet, Shang Cai explained the process. “The journey of tumor cells that trigger metastasis is very difficult. They go through a series of stresses during this process”, she says. “One of them has to do with the passage of these cells through the blood vessels, which can be turbulent and lead to their death.” To understand what happens, it is possible to imagine that the cells, in the passage of blood, are thrown against the walls of arteries and veins, suffering shocks that can damage them.

However, the research revealed that the presence of bacteria is capable of strengthening the cytoskeleton of tumor cells, that is, the fiber network that gives shape to them. With this, they can better withstand the stress of passing through blood vessels. “It is something that greatly increases the survival rate of cancer cells and, ultimately, gives rise to metastases”, says the researcher.

According to Cai, it is still not possible to imagine that a simple treatment with antibiotics will be able to minimize the chances of the appearance of metastases. Without the right combination of drugs, the use of antibiotics could even select bacteria that are more capable of inducing metastases. “How to modulate intratumoral bacteria is an important scientific question that will require further analysis”, he ponders.