Today, the leading academic journal, Science, publishes a new paper on cancer research. A team of researchers led by the Weizmann Institute of Science in Israel found that there are many bacteria in human tumors. Even more amazingly, these bacteria appear to be tumor-specific – different tumor samples, and the types of bacteria are distinguished. This work is important for understanding the microbiome of tumors, and it is also on the cover of this issue of Science.
Picture: V. Altounian/ScienceDaily
Scientists have detected bacteria in human tumors more than 100 years ago, the researchers note in their paper. Some believe this suggests that bacteria may have a local role in the tumor’s microenvironment, while others point out that the bacteria are so low that it is difficult to confirm whether they are actually from tumor samples or from outside contamination.
In this study, scientists have done the most rigorous and comprehensive analysis to date to truly understand the role of bacteria in human tumor samples. To reduce the potential problems posed by external contamination, they used a variety of different methods, not only using 16S rRNA gene sequencing techniques to find bacteria, but also with microscope observation and cell culture to identify different bacteria living in tumors.
The researchers analyzed seven common solid tumors (Photo: Supplied)
The researchers analyzed seven common solid tumors, including breast, lung, melanoma and pancreatic cancer, with more than 1,500 samples. The results of the analysis confirmed that most of the samples contained bacteria. Surprisingly, most of the bacteria found in these tumors are inside the cell! Whether it’s cancer cells or immune cells, researchers have found bacteria in their bodies.
Studies have shown that most of these bacteria are located in cells. Pictured are 2 bacteria (arrows) observed in breast cancer samples (Photo: Supplied)
The types of bacteria vary for different tumor types. The researchers point out that different tumors have different microbiome compositions. In contrast, the microbiome of breast cancer tumors is more diverse and abundant. In addition, the researchers note in their paper that the bacteria are also associated with the patient’s history of smoking and their response to immunotherapy.
Different types of bacteria in different sample tissues (Image Source: Resources 1)
The journal Science has made a separate monograph for this paper. The interpretation raises several key questions, one of which is: Why do bacteria be found in tumors?
The scientists made several assumptions about this problem. The first hypothesis is that human tissue may not be as “sterile” as we thought, but that there will always be a small amount of bacteria. The detection of certain toxin-producing bacteria may indicate that the cells are in an inflammatory state, which may promote cancer. And when the tumor does appear, on the one hand will destroy the surrounding tissue, on the other hand will inhibit immunity, which in turn promotes bacteria in the body, run to what should be sterile location.
Other issues were also mentioned in the interpretation of the Science article (Image Source: Resources Resources)
Of course, given that many bacteria are present in cells, another possibility is that these bacteria cannot “freely” flow to tumors and surrounding tissues, but are “carried” by other immune cells and/or cancer cells.
In this interpretation, the authors also point out that even if these bacteria are associated with the occurrence of tumors, it is difficult to target these bacteria effectively. Typically, we intervene with bacteria through diet, drugs, or other microorganisms. But we don’t know if we can do the same thing against the bacteria that live in the tumor. They may rely entirely on cells for nutrients, and it is difficult for general antibiotics to get into the cells to kill them.
This study also appeared on the front page of Science’s official website (picture source: Screenshot of Science’s official website)
Even if there is no good sterilization method, this study is extremely important. A better understanding of the microenvironment of tumors can provide a better understanding of the mechanisms in which cancer occurs and progresses. This promises to lead to new and precise treatments and diagnostics.