Dor years, there has been growing evidence that bacteria are linked to cancer, and sometimes even play an important role in its progression. Now researchers have discovered a similar link with another type of microorganism: fungi.
Header image: yeast culture candida. (William Kaplan/ CDC)
Two studies conducted this week highlighted the unique presence of fungal species living inside tumors. It’s possible that they can even influence the way cancers grow or manage to counter certain treatments.
Since the 19th century, scientists have known that bacteria and other microscopic organisms regularly live on or in our bodies, usually without making us seriously ill. But it is only in recent decades that the value of these microbial communities, or microbiomes, for our well-being and our health began to be recognized. And it’s only more recently that we’ve started to look closely at the microbiomes in cancers.
Most of the early research on cancer microbiomes focused on bacteria. But although fungi are less abundant in the human body, they are thought to play a vital role in how microbiomes influence our health. These new studies, both published this week (links below), are among the first to attempt to create a rough map of the fungal microbiome present in our cancers.
One such study involved researchers from the University of California-San Diego School of Medicine as well as theInstitut Weizmann des sciences in Israel. By examining more than 17,000 blood and tissue samples taken from cancer patients, they were able to find low levels of the fungi in 35 different types of cancer.
According to study author Rob Knight, a researcher and professor at UC San Diego:
The existence of fungi in most human cancers is both surprising and predictable. It’s surprising, because we don’t know how fungi might get into tumors through the body. But it’s also expected because it fits the pattern of healthy microbiomes throughout the body, including the gut, mouth, and skin, where bacteria and fungi interact as part of a complex community.
In the different types of cancer, the microbiomes showed different types of fungal species, but Knight and his team noticed some common features. These fungi generally appeared to be intracellular, meaning they live inside cancer cells. They also found evidence that the fungi and bacteria present in these cancers commonly interact with each other, and rarely in a competitive way. Importantly, the team found associations between these fungal microbiomes and aspects of cancer itself, such as its response to cancer treatments.immunotherapy.
The other study was conducted by researchers from Duke and Cornell universities (USA). This team also found many fungi nested in human cancers, with some more likely to harbor this type of fungi than others. In lung cancer tumors, for example, Blastomyces fungi were more frequently found, while fungi Candida were more common in gastrointestinal cancers. The presence of these particular fungi was also linked to a lower chance of survival for patients with these cancers.
At this point, these results only show a correlation between the fungal microbiome and the consequences of cancer, not a direct causal relationship. And while the microbiome, in general, is important to human health, we are still only at the very beginning of studying exactly how it affects us, let alone how to repair a microbiome that has become harmful. But this research will allow scientists to better understand the complex biology of cancer and, perhaps one day, create better treatments for this disease.
The study published in the journal Cell: Pan-cancer analyses reveal cancer-type-specific fungal ecologies and bacteriome interactions and presented on the Weizmann Institute of Science website: Human Tumors Are Prized Real Estate for Fungi, Study Finds.