Our bodies and tumors are home to many microbes. Over the past 5 years, researchers have shown that cancer tissue contains colonies of many different types of organisms. Some of thebacteria may be related to the disease. In a paper published in Nature this week, a team led by Susan Bullman of the Fred Hutchinson Cancer Center reported that in oral and colorectal tumors,bacteria live inside and boost their production of proteins that suppress the immune system. The immune system may not be able to kill cancer cells if the interlopers set off a chain reaction.
The study doesn't completely rule out the possibility of abacterial involvement in cancer, but it is suggestive. She says that it shows that the immune equilibrium can be disturbed.
Confirmation thatMicrobe can cause tumors to grow or spread could open up new ways to make cancer treatment more effective. Researchers are looking into the possibility of using microbes to detect cancer in a blood sample.
Cancer researchers used to think tumors were sterile, according to a researcher at the Weizmann Institute of Science. When he was a PhD student at the Broad Institute, he discovered that human cancer cells grown in the lab stopped responding to a cancer drug when Mycoplasmabacteria were present in the culture. He found that thebacteria protected the cells by breaking down thecitabine.
The drug gemcitabine could be rendered useless in mice with colon cancer if they were injected with other types ofbacteria and treated with antibiotics. He foundbacteria that produced the drug-chewing enzymes in 75% of the human pancreatic cancer samples he studied. A clinical trial is planned to see if antibiotics can improve the treatment of Pancreatic Cancer.
Gregory Sepich-Poore, a PhD student in Rob Knight's lab at the University of California, San Diego, was looking for ways to diagnose Pancreatic Cancer early. He was motivated by the death of his grandmother, who was diagnosed too late for treatment and died of cancer. Sepich-Poore started looking at the Cancer Genome Atlas for snippets of genetic material from microbes.
He, Knight, and colleagues reported in March 2020 that the different types of cancer they studied had different types of microbes. The team was able to find signatures in blood samples from cancer patients. Micronoma is a startup based in San Diego that aims to identify early-stage cancer in blood samples.
Many tumors have unique populations of microbes that reside inside cancer and immune cells, rather than between those cells, according to a study done in 2020.
This paper has taken the field a big step forward.
Fungi live in tumors. In a study of 17,000 tumors, published in Cell in September, the UCSD and Weizmann groups found a number of different types of fungi. Each cancer type was associated with a different species, which could help refine Micronoma's diagnostic tools. He is now on the company's scientific advisory board.
In ovarian and breast cancer, certain combinations of fungal species correlated with lower odds of survival. A group reported in October that the presence of a particular bacterial signature seemed to accelerate the death of patients with Pancreatic Cancer. Patients that did not have the signature had a doubled chance of surviving. Martin Blaser is a cancer researcher at Rutgers University and sits on Micronoma's scientific advisory board.
None of these findings showed how a bad outcome could be caused by the same organisms. Bullman and her colleagues studied tumors from patients with oral cancer and colorectal cancer. They only colonized certain areas of the tumors. These regions were found to have high levels of the cancer-fighting T cells. T cells were found outside but not inside. The regions contained a type of immune cell called neutrophils. The T cells may be moving away from the tumor because of thebacteria.
In a study using a technique called single cell sequencing, the researchers found that Fusobacterium and Tremabacteria were preferentiallyinfecting cancer epithelial cells, which line the inside surface of organs, and that only cells in which the twobacteria were dominant tended to show both immunosuppressive and cancer promoting
George Miller is a cancer doctor and researcher at Trinity Health of New England.
Bullman and her colleagues cultured Fusobacterium species with colon cancer spheroids and compared them withbacteria-free spheroids. The cancer cells were the same as they were in the patient tumors. Bullman thinks that the cancer cells breaking off the spheroids is a sign that they are meetingastasizing.
The paper paints a plausible picture of howMicrobe could affect the body's defense against cancer. She cautions that the spheroid model is a reductionist approach and that the human body may have other mechanisms that keep cancer at bay.
The study only included two types of cancer and left a lot of work to be done. He says thatBullman's research has shown how we should be looking at the tumors. The paper has made a huge step forward.
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