Radiotherapy and the microbiome: could a patient’s ‘gut group’ change their response to treatment?

Most of us know our blood group. It’s taken early in our life and stored in our patient record, and it’s important that should we ever need a blood transfusion, doctors know what it is. Our blood type is based on whether one, both or neither of two sugar molecules, referred to as A and B, are present on the surface of our red blood cells. There’s A, B, AB and the most common type, 0, which means neither are present.

But what if we could use a similar system to classify our gut bacteria? And what if people with different ‘gut groups’ could have different medical needs?

Communities of bacteria and other organisms, including viruses, have evolved in tandem with us over millions of years. Although they account for only a tiny fraction of our weight, there are about 10 times more non-human cells than human cells in the human body, and a healthy ‘microbiota’ carries out functions from producing vitamin K to fighting off potentially harmful bacteria or viruses.

Although healthy people are known to have similar gut floras, evidence suggests that they may be divided into three groups according to their intestinal bacteria, called ‘enterotypes’. One is enriched in a type of bacteria called Bacteriodes, the second in Prevotella, and the third in Ruminococcus.

Some gut bacteria are known to be relevant in cancer – for example, the link between Helicobacter pylori and stomach cancer has long been known. Some bacteria such as Roseburia or Eubacterium seem to have beneficial effects by producing molecules such as butyrate, which may protect us from harmful side-effects of radiotherapy.Helicobacteria

Gut bacteria and radiotherapy

This week saw the publication of an article in The Lancet Oncology from a team led by Professor David Dearnaley and Dr Jervoise Andreyev, here at The Institute of Cancer Research in London and The Royal Marsden NHS Foundation Trust. The article applies principles from the study of the microbiome – one of the most cutting-edge areas of current science – to cancer care.

Professor Dearnaley, an expert in radiotherapy, is interested in reducing the side-effects it can cause in some patients. Among these side-effects, radiotherapy to the abdomen can cause gut problems, which sometimes arise soon after treatment, but can also take longer to develop. Professor Dearnaley’s team argue in the Lancet Oncology article that these gut problems show a remarkable similarity to inflammatory bowel disease, which has well-known links to disturbances in gut flora. It seems that bowel problems after radiotherapy may be caused at least in part by their effect on the bacteria that live there.

Bacterial treatments?

A fascinating question – which our scientists aim to explore – is whether profiling the gut ecosystem could help inform patient care. The ultimate aim would be to effectively manipulate the gut ecosystem as an actual treatment for intestinal problems after radiotherapy. Beneficially altering the make-up of our gut flora is still an emerging discipline but, for example, a study has already shown that transplanting faeces from healthy donors into patients can effectively treat recurrent Clostridium difficile infection which does not respond well to antibiotics. This treatment method has also been shown to have an effect in inflammatory diseases of the bowel unrelated to infections.

The terms ‘microbiota’ and ‘microbiome’ have only been around since the turn of the 21st Century, and the detailed study of the gut flora in relation to human health is relatively new. The work of researchers here at the ICR and The Royal Marsden could represent the first steps towards personalised cancer treatment based on the ecosystem of microscopic inhabitants of our bodies.

For further reading on recent developments in our understanding of the effect of the microbiome on human health, see this briefing from the Medical Research Council.

Image credit B0004847 David Gregory&Debbie Marshall, Wellcome Images: Creative Commons by-nc-nd 2.0 UK: England & Wales. The image is a scanning electron micrograph of a colony of Helicobacter bacteria.

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