Cancer patients respond best to treatment when they have the right cocktail of bacteria in their guts, research indicates.
Two separate studies have found the "microbiome" of the gut - the bacteria, viruses and other bugs in the digestive system - can determine whether tumours will shrink when treated with immunotherapy drugs.
The studies carried out by scientists in the US and France relate to PD-1 inhibitors, which prevent tumours hoodwinking the body's immune system into thinking they are healthy cells.
Both found certain gut bacteria can boost the likelihood of a patient responding to a drug, Science magazine reports.
PD-1 inhibitors can hold certain cancers at bay for many years but only about 25 per cent of patients respond to the drugs.
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Now, the teams behind both studies are hopeful this figure could be boosted significantly if they are able to manipulate the make-up of gut bacteria.
The team at the Gustave Roussy Cancer Campus in Paris also discovered that immunotherapy patients taking antibiotics, which disrupt gut bacteria, relapsed sooner or did not live as long as others.
Immunologist Laurence Zitvogel, the leader of the study, believes that by simply avoiding antibiotics the number of patients responding to immunotherapy could be boosted to 40 per cent.
In the US, Jennifer Wargo, of the MD Anderson Cancer Centre in Houston, Texas, found patients with a more diverse range of bacteria in their gut and more specific bacteria were more likely to respond well to the treatment.
She plans to test whether altering the gut's microbiome with faecal transplants in pill form or bacterial treatment could help melanoma patients respond to PD-1 blockers.
