Written by Aaron Khemchandani, Science Writer.
The link between bacteria and cancer has long been evidenced by researchers. Now, however, scientists have unearthed a comparable connection between cancer and another type of microorganism that is ever-present in our food, in our surroundings and in our bodies – fungi.
A new connection
The presence of certain fungal species in various types of cancer tumours can predict and may even drive negative cancer outcomes, according to a pair of new studies published in the journal Cell. These findings could help us uncover several oncogenic mysteries and, ultimately, influence the development of future cancer treatments.
Fungal microorganisms, much like bacteria, comprise a vital part of the human microbiome. The idea that bacteria can accelerate cancer development has been strongly evidenced in a large number of scientific studies. However, little is known about the oncogenic roles of fungi – which, like bacteria and viruses, colonise a number of our tissues, interact with the immune system and have the capacity to cause disease. Now, two recent studies have published crucial discoveries that bring some aspects of fungal impacts on tumour progression to light.
Unearthing microbial mysteries
In one of the studies, researchers from the Weizmann Institute of Science in Israel systematically profiled fungal communities in more than 17,000 human tissue and blood samples representing 35 different cancer types. As the scientists expected, fungi was detected in all of these cancers. However, the makeup of these populations varied from one cancer type to another; the importance of this variation was outlined by links between the presence of specific fungi and differences in tumour growth.
For example, breast cancer patients with Malassezia globosa – a fungus that has been associated with pancreatic cancer – in their tumours had far lower survival rates than those who did not have it, while ovarian cancer patients with intratumoural Phaeosphaeriaceae fungi had significantly shorter progression-free survival periods.
The researchers also characterized bacterial microbiomes in the tumours and, interestingly, found that most fungal types tended to coexist with certain bacterial species. This meant that tumour environments may favour the growth of both fungi and bacteria, and this behaviour differs from what is seen in typical environments where fungi and bacteria tend to compete for resources and hamper overall growth.
Pronounced impacts on survival
In another study, a team of immunologists at Weill Cornell Medicine Medical School analysed tumour environments in gastrointestinal, lung and breast cancers, finding that they each contain different levels of specific fungal species and that the presence of certain fungi correlated with worse disease outcomes. Researchers examined the Cancer Genome Atlas, the largest detailed genomic database of human tumours, with the most prominent observation being that high levels of Candida in gastrointestinal tumour cells were linked to increased inflammation and metastasis as well as lower survival rates.
The scientists suggest their findings may one day allow for specific fungi in tumour biopsies to be used as diagnostic or prognostic biomarkers, indicating factors such as potential metastatic risk.
Where do we go from here?
Both sets of findings establish the clearest link yet between cancer and fungi, and this research opens the door for different approaches towards the development of new cancer therapeutics. However, more research is needed to understand the intricacies of fungal involvement. How exactly do specific fungi promote inflammation and metastasis in certain cancers? Why do some fungi greatly accelerate tumour progression in some cancer types but not others? Although many questions remain, this novel research has provided an exciting foundation from which they may be answered.