The hunt is on to learn why bowel cancer in young people is rising

One of the most concerning trends in cancer is the rising incidence of several types of tumour in people under 50 – something that is especially marked for bowel cancer.

Now, a £20-million, five-year research project that aims to discover the cause of rising bowel cancer cases has got the go-ahead. It will use stored samples of blood, urine and faeces from millions of people from about 15 biobanks in Europe, North America and India.

The goal is to understand whether the rise is connected to changes in food, drink, medicines, air pollutants or other environmental chemicals, by measuring everything people are exposed to – known as their “exposome”.

“The exposome is all elements of our external world that have impacts on our health,” says Andrew Chan at Massachusetts General Hospital in Boston, co-leader of the project.

The number of people under 50 diagnosed with bowel cancer has been going up for three decades. In the UK, for instance, there has been about a 50 per cent rise in these tumours in people aged 25 to 49 over this period, with similar trends in the US, Canada, Australia and several European countries.

As about 9 in 10 tumours happen in older people, the rise in the under-50s hasn’t yet had much impact on the total number of cancer deaths. But the trend is concerning doctors, especially because tumours in younger people can be more aggressive and tend to be diagnosed at a later stage.

There has been much speculation about the cause, with key suspects being various aspects of the modern diet – such as our rising consumption of processed food or red meat, or a lack of fibre – along with antibiotic use or pollutant exposure.

In the new research project, Chan and his team will investigate further by trying to identify and measure all the chemicals in medical samples from previous studies.

They will use mass spectrometry to identify chemical signatures of novel compounds that have entered the body or disturbed levels of natural biochemicals.

One of the biobanks being used is the Nurses’ Health Study 3, a large US project charting the health and lifestyles of hundreds of thousands of nurses. A subset of participants donated stool samples as well as blood samples, which will also let the team analyse their gut bacteria.

Another important cohort will be the Danish Newborn Screening Biobank, which contains a dried spot of blood from virtually all babies born in Denmark since 1982, with nearly 2 million samples. This will let researchers see if anything we are exposed to in the uterus is linked with higher bowel cancer risk.

If, as hoped, correlations emerge between certain biochemicals in the blood and the risk of bowel cancer, the team will investigate if blood tests could identify people who are more vulnerable, says Chan. “That could be a group of individuals we target with more intensive bowel cancer screening,” he says.

Another part of the project will test if a targeted diet can reverse blood and gut bacterial signatures linked with bowel cancer risk, says Jordana Bell at King’s College London, one of Chan’s collaborators. “We will try to apply these insights that we generate early on, by identifying putative causal factors, understand potential mechanisms and design intervention trials,” she says.

Iain Foulkes at Cancer Research UK (CRUK) says: “In the US, recent data shows that people born in the 1990s have a 2.4 times higher risk of colon cancer than those born in the 1950s. While most cancer cases are in people over 50, this development is an important one for us to address. The key is understanding why the rise in early-onset cancers is happening in the first place.”

CRUK is funding the work along with the National Cancer Institute in Maryland, France’s Institut National du Cancer and the Bowelbabe Fund in the UK.