If you search for images of tumors on Google, you may see clusters of brightly colored cancer cells against a dull background of healthy tissue. But the situation looks very different for Leanne Narnski-Haziza, a cancer biologist at the Weizmann Institute of Science in Israel. A tumor may contain millions of microorganisms representing dozens of species.
“I think it’s an ecosystem,” she said. “It means cancer cells are not alone.”
Scientists have long known that our bodies are home to microbes, but have tended to treat tumors as if they were sterile. It turns out that tumors are infested with microbes.
In 2020, several research teams showed that tumors are inhabited by a mixture of different bacteria. and on thursday 2 the study Published in the journal Cell, found that tumors are also home to many species of fungi.
This so-called tumor microbiome has proven to be so distinctive for each type of cancer that some scientists believe that by measuring the microbial DNA that tumors shed into the blood I’m trying to find early signs of a tumor. Also, some studies suggest that microbes may make tumors more aggressive or more resistant to treatment. By attacking the tumor microbiome, it may be possible to fight cancer.
“We need to reevaluate almost everything we know about cancer through the lens of the tumor microbiome,” said Ravid Straussman, a cancer biologist at Weizmann who collaborated with Dr. Narunsky Haziza on one of the new studies. rice field.
For the past 20 years, scientists have microorganism It is taken into the human body by taking DNA from mouth swabs, skin scrapings, and feces. These studies have identified thousands of species that live harmlessly in the body of healthy humans. 38 trillion cellsmany organs once thought to be sterile It turned out to have its own microbiome.
Researchers have explored the healthy microbiome, but cancer has been largely uncharted territory. No one knew whether the millions of cells that make up a tumor provide another possible habitat for microbes.
In 2017, Dr. Straussman and his colleagues encountered bacteria living within pancreatic tumors. They made this discovery while racking their brains over how some tumors were able to resist chemotherapy drugs. It turns out that he lives inside.
This discovery led Dr. Straussman and his colleagues to conduct a large-scale survey of bacteria in more than 1,000 tumors from seven types of cancer. In 2020 they report Discover the fungi hidden in all seven types.
Around the same time, a team of researchers at the University of California, San Diego, conducted their own search using a huge database of DNA collected from different types of cancer in the early 2000s.
The project, called the Cancer Genome Atlas, was intended to help scientists find mutations in oncogenes that cause cancer cells to grow out of control. However, the San Diego team realized that the raw data could also contain DNA from bacteria within the tumor.
Unfortunately, that meant sifting through the 6 trillion gene fragments in the Atlas looking for pieces of bacterial DNA.
“It’s like trying to find a needle in a haystack when there are more straws of hay than stars in the Milky Way,” says team member Gregory Sepich-Poore.
The search took years, but it paid off. Dr. Sepich-Poore and his colleagues found that a small percentage of his DNA fragments in 32 types of cancer belonged to bacteria, not humans.
After a researcher publishes a paper study In 2020, we worked with Dr. Straussman’s team to see if the tumors also contained fungi.
Fungi are one of the great success stories in evolutionary history. 6.2 million speciesThey include the mushrooms that grow in the forest, the yeast that ferments bread and beer, and the mold that gave us penicillin.
One characteristic that all fungi have in common is their eating habits. They spew enzymes to break down nearby organic matter and soak it. Fungi are also capable of producing vast numbers of spores that can survive for years in all kinds of extreme conditions.
We are constantly exposed to fungi, either by picking up spores on our skin or by eating food that fungi are hitchhiking on. Most of them never live in our bodies.
“A lot of things are just passing by,” said Ilyan Illiev, an immunologist at Weil Cornell Medicine in New York.
However, some species have adapted to live inside our bodies. Skin fungi break down the oils we make. Others feed on sugars in the mouth and digestive tract. Scientists have also discovered other fungi in our bodies whose life remains a mystery. “We really don’t know a lot,” said Dr. Iliev.
Researchers from San Diego and Weizmann have returned to the galaxy of DNA fragments in the Cancer Genome Atlas, looking for fungi in tumors much the same way they look for bacteria. Only this time, they looked for fungal genes. We also examined Dr. Straussman’s tumor collection.
Of the 35 types of cancer the scientists examined, all types of tumors contained fungi, and each type had a characteristic combination of fungal species. report One of the studies published Thursday.
In another new report, Dr. Iliev and his colleagues independently found Tumor fungus from seven body parts: mouth, esophagus, stomach, colon, rectum, breast, lung.
Deepak Saxena, a microbial ecologist at New York University who was not involved in either study, was surprised by the scale of the findings. I didn’t,” he said. “This will change the way we think.”
Dr. Sepich-Poore and some of his colleagues in San Diego founded a company called Micronoma to turn their research into blood tests for cancer. They say that by looking at the DNA shed by fungi and bacteria within a tumor, they can accurately predict what type of cancer the microbe originated from.
They don’t know why the test works. Geography may be part of the answer. Lung tumors tend to attract microorganisms already in the lungs. However, some microbes migrate to new organs and get inside the tumor.
Both new studies found microbes that appear to be associated with worse cancer outcomes. For example, Dr. Iliev and his colleagues found that people were more likely to die from stomach cancer if their tumors contained a fungal species called Candida tropicalis.
Some microbes not only stay within the tumor, but may help the tumor grow. There is a possibility that
Jessica Galloway-Peña, a microbiologist at Texas A&M University who was not involved in the new study, cautioned that this study alone cannot prove whether microbes have such an effect. Scientists have to do experiments on cancer cells in dishes and animals.
“Okay, it’s related to certain types of tumors, but is that just living with the tumor, or is it actually making it grow and progress?” Galloway – asked Dr. Peña. “You just don’t know at this point.”