Why is colorectal cancer rising in younger age groups?

A new study has confirmed that the rate of colorectal cancer is rising in younger adults around the world, with England among the countries seeing the highest increase.

The paper in The Lancet Oncology used World Health Organization (WHO) data on colorectal cancer in people aged less than 50 to gauge the trend in incidence in this group versus older individuals.

The worrying finding was that early-onset colorectal cancer is on the rise in 27 out of 50 countries, typically advancing at a rate that outstrips cases in older patients, and stable in the remaining 23.

It is the first study to track a rise in early-onset bowel cancer outside high-income Western countries, including regions like Latin America, the Caribbean, Eastern Europe, and Asia.

The analysis found that England experienced the fourth fastest rise in the rate of early-onset bowel cancer in the decade to 2017 – at 3.6% per year – behind only New Zealand, Chile, and Puerto Rico, and just ahead of Norway.

The increase was most apparent in women in some countries, including England, but was seen most often in men in Puerto Rico and others – just one finding that leads the researchers behind the work to acknowledge that the reasons for the trend are hard to fathom. Notably, the increase seen in England was not matched in the other UK nations.

So, what could be behind the trend? Previous studies have suggested a wide range of risk factors for this type of cancer, including prolonged sitting, poor diet, consumption of sugary drinks and alcohol, as well as illnesses like obesity and diabetes.

The authors of the study note that, in many of the newly identified countries, increases in early-onset colorectal cancer seem to coincide with or follow on from periods of economic development, which they suggest could be linked to rapid changes in lifestyle and diet.

"Early-onset colorectal cancer is a growing global phenomenon, But, at the same time, it is still rare," said Dr Yin Cao from Washington University in St Louis, one of the researchers behind the work. "Even though it is increasing, I don't think people should be scared."

A commentary on the paper from Cancer Research UK noted that changes may have happened earlier and more gradually in countries like the UK and the US, where the increases in early-onset colorectal cancer rates had already been documented, and changing rates could also be affected by changes in how and when the cancer is diagnosed.

"More research is needed to understand whether there are genuine differences between the nations, and how to address them," said Katrina Brown, a senior cancer intelligence manager at CRUK.

Overall, it's worth noting that the UK nations have a mid-table ranking of 16th to 19th for the overall rate of this type of cancer, and the charity thinks the regional differences between the devolved nations may be down to population differences.

Cao said the differences underscore the need to identify emerging and novel risk factors for early-onset colorectal cancers, which might mark them out from cases that start later in life.

It's a view echoed by Dr Sarah Bailey, of the University of Exeter Medical School in the UK and an advanced fellow at the National Institute for Health and Care Research (NIHR), who was not involved in the study.

"This high-quality study confirms that colorectal cancer rates are rising in younger adults in many countries," she said. "The reasons for this are not fully understood, but it is clear that we need to be searching for the underlying causes."

Bailey also pointed out that earlier diagnosis strategies for colorectal cancer, such as screening programmes and investigation of symptomatic patients in primary care, tend to target people aged 50 and over – the age range in which most new cases are diagnosed.

"As rates in younger adults increase, we will need to explore how we can expand our strategies to capture cases early in this group too."