It is thought some strains of bacteria may cause cancer or allow it to develop unchecked

Bowel cancer patients will be given a groundbreaking form of treatment aimed at altering the makeup of their gut bacteria, in a trial due to launch this year.

The phase one trial, backed by a £20m grant from Cancer Research UK, is led by an international team who are investigating whether gut bacteria play a role in triggering cancer and making the disease more resistant to treatment in some patients.

Prof Wendy Garrett, of the Harvard TH Chan School of Public Health and a co-leader of the project, said that in future treatments to reset the microbiome or subtly alter it could be used alongside conventional cancer drugs.

“Everybody involved in this project wants to improve outcome for patients with bowel cancer and ultimately we want to prevent it,” she said.

The human gut contains trillions of bacteria, which play a crucial role in digesting food and strengthening the immune system. But there is emerging evidence that certain strains of bacteria may be involved in triggering cancer, in allowing it to develop unchecked, or in making cancers resistant to chemotherapy and other treatments.

The initial trial, which is expected to involve a dozen patients, will investigate the potential for using faecal transplants to reset the gut of patients by reducing the presence of cancer-associated microbes.

The procedure involves transplanting a stool sample, along with the microbes it contains, from a healthy donor. The trial will focus on safety and side-effects.

Previous work by Garrett and the project’s other co-leader, Prof Matthew Meyerson, also of Harvard, has revealed that gut bacteria look different in bowel cancer patients. One study found that a microbe called Fusobacterium nucleatum was more common in cancerous tissue and in cancer patients than in healthy people.

When mice that were predisposed to developing cancer were exposed to this bacteria, tumours occurred more quickly. “Maybe this bacterium has a role in enabling bowel cancer or taking the brakes off bowel cancer development,” Garrett said.

One theory under investigation is that the bacterium sticks to pre-cancerous cells and shields them from being spotted by the immune system. This could potentially leave them to spiral into a cancerous state and form a tumour.

Studies have also shown that certain so-called good bacteria are more common in patients who respond to both chemotherapy and new immunotherapy cancer treatments.

Bowel cancer is the fourth most common cancer in the UK, accounting for 12% of all new cancer cases in 2015. A range of lifestyle factors have been shown to influence people’s risk of developing the disease, including diet and obesity.

Meyerson said the project, which involves collaborators in Canada, the UK, Spain and the Netherlands, would look at whether changes in gut bacteria linked these lifestyle factors. The team will also try to answer whether the “bad” bacteria are causing bowel cancer or simply thrive in a cancerous environment.

“Maybe this is going to be incredibly important for the understanding and treatment and prevention of bowel cancer,” said Meyerson. “Maybe it’s just going to be a phenomenon that’s there. Until we answer a lot of questions, we won’t know.”

The project will look into other potential future treatments, including antibiotics and vaccines that would trigger an immune reaction against targeted microbial communities in the gut.

At present, Meyerson said, screening remained the best known way to improve outcomes for bowel cancer patients, because treatment is most effective during the early stages of disease. “If there’s a lesson the average person needs to know about bowel cancer, that’s probably it,” he said.

The project is being funded as part of Cancer Research UK’s Grand Challenge initiative, under which the charity will give major grants to US institutions for the first time.

Michelle Mitchell, the charity’s chief executive, said: “To reach our ambition of three in four people surviving their cancer by 2034, we need to collaborate not only with researchers from across the globe but with funders in other countries who share our goals.”