It found a 1.8% increase in colon cancer cases and 1.4% rise in rectal cancer cases in people under 50 in the UK between 1995 and 2014 .
Over the same period, there were decreases in bowel cancer cases of 1.2% in the over-50s.
The findings were similar in many of the countries studied.
Dr Marzieh Araghi, lead study author from International Agency for Research on Cancer in Lyon, said the findings highlighted the need for action.
While population-based screening in people under 50 years old is not considered to be cost-effective due to relatively low incidence numbers, family history could help to identify younger people at high risk of genetic susceptibility to colorectal cancer, for further assessment,” she said.
Dr Araghi added that more studies were needed “to establish the root causes of this rising incidence to enable the development of effective preventive and early-detection strategies”.
‘Red flag’ symptoms
Andrew Beggs, consultant colorectal surgeon from the University of Birmingham, said rising rates of bowel cancer among young patients “must be urgently investigated”.
“This means the age at which bowel cancer screening needs to start may have to change to screen people at a younger age, and people under the age of 50 with any ‘red flag’ symptoms (bleeding, a change in bowel habit, weight loss or tummy pain) should get it checked out as soon as possible,” he said.
a persistent change in bowel habit – going more often, with looser stools and sometimes tummy pain
blood in the stools without other symptoms, such as piles
abdominal pain, discomfort or bloating always brought on by eating – sometimes resulting in a reduction in the amount of food eaten and weight loss
“These large and high-quality studies provide solid data to support this trend,” he said.
And he added: “These results are a call to action to raise awareness among staff in GP practices and hospitals to consider bowel cancer as a diagnosis when young people come to them with pain, changes in bowel habits or blood in their stool.
“The new studies show a clear need to dedicate more efforts to understanding the lifestyle factors that trigger bowel cancers in young people and to rethink how screening may need to be adjusted to prevent such devastating cancers.”