The microbes that surround and infiltrate cancer tumours may help predict how a person’s disease progresses and which drugs they are most likely to respond to. A better understanding of this “tumour microbiome” may also lead to new cancer treatments.
Cancer tumours are laced with bacteria and viruses. These can be found inside the cells, between them and in the space surrounding them. Until a few years ago, researchers assumed these microbes had ended up in tumours as a result of handling cells in the lab and were merely a sign that the samples had been contaminated, says Eytan Ruppin at the US National Cancer Institute in Maryland.
More recently, researchers have come to learn that these microbes, said to form a tumour’s microbiome, may play a role in how a cancer forms, develops and spreads. Research on gut bacteria has shown, for example, that microbes seem to interact with a person’s immune system and can influence how metabolism works. Could microbes influence cancer in the same way?
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Earlier this year, Rob Knight at the University of California San Diego and his colleagues assessed the presence of microbes in around 18,000 tumour samples, taken from more than 10,000 people with 33 different types of cancer.
The team found that the presence of certain types of microbes was associated with specific cancer types. Based on the presence of bacteria alone, the researchers were able to .
Ruppin wondered whether the presence of microbes might also predict how well people with cancer respond to treatment and how likely they are to survive the disease. To find out, he and his colleagues turned to some of the same data used by Knight’s team.
The researchers developed a model that was fed data about the participants’ cancer type, as well as the length of time before the person’s cancer progressed and how many years they lived after their diagnosis. By training their algorithm on this data, they were able to use the presence of bacteria to predict survival.
Although the prediction was only correct around 60 to 70 per cent of the time, the results were more accurate than clinical estimates based on a person’s sex, age and tumour stage, says Ruppin.
They also looked at whether the presence of some microbes might influence how well tumours respond to drug treatment. The researchers specifically assessed the impact of 30 drugs on the size of tumours and how long people survived once they had started treatment. For five of these drugs, the algorithm could predict how well the tumour responded to drug treatment.
The test isn’t yet accurate enough to be used clinically, but Ruppin hopes that analyses of tumours’ microbiomes might improve the accuracy of “liquid biopsies” – tests currently being developed to diagnose cancer based on tumour cell fragments or DNA in the blood.
As we learn more about the roles of microbes in the progression of cancer, we might be able to develop new cancer treatments that specifically target the tumour microbiome, says Ruppin. “If, further down the road, we learn that specific bacteria play a role in the progression of cancer, we could treat it with targeted antibiotics,” he says.
In the meantime, researchers must first understand exactly what the microbes are doing, as well as how they affect the growth of tumours and their response to drug treatments. “We still need to figure that out,” says Ruppin.
bioRxiv
