There has been a shift in colorectal cancer rates towards people under the age of 50, but lowering the age of screening may be premature, a provocative session at DDW 2018 was told.
Coming just three weeks after the American Cancer Society recommended lowering the age of colorectal cancer screening from 50 to 45 years of age, the session explored the possible explanations for an ‘epidemic’ of early-onset colorectal cancers and also the evidence for how to manage the trend.
Dr Rashid Lui of the Chinese University of Hong Kong, said that colorectal cancer rates in the US were declining in the screening age group over 55 years of age, but increasing among people under the age of 55. He noted that most of the increase was being seen in the 40-50 age groups and the overall numbers were still low, at about 20% of the rates seen in people over 70.
Nevertheless, similar trends were seen in data he presented from international cancer registries covering countries such as the UK, Hong Kong and Sweden, and there were also increases being seen in rates of colorectal cancer resections among younger age patients, the conference was told.
Dr Stuart Po-Hong Liu, a gastroenterologist and researcher at the Massachussets General Hospital presented data from more than 85,000 women in the Nurses health Study linking younger-onset colorectal cancer to rising rates of obesity.
The risk of colorectal cancer at a young age was linked to higher BMI at age 18 and also to weight gain from the age of 18, he said. It was notable that almost 20% of the cases of early-onset colorectal cancer were seen in people with a BMI over 30, he noted.
Other study findings presented at DDW 2018 showed that only 25% of the cases of young-onset colorectal cancer would be picked up under current screening criteria for people aged 40-50, based on family history. This suggested a need to review colorectal cancer screening policies for younger people, the study authors said
The recent recommendation by the American Cancer Society (ACS) that people at average risk of colorectal cancer start regular screening at age 45 was based on an analysis of data of the rising incidence among young adults, said Elisabeth Peterse of the Department of Public Health at Erasmus University Medical Center, in Rotterdam, the Netherlands.
Modelling showed that lowering the age of screening to 45 years of age would have a favourable balance of benefit to risk, in terms of colorectal cancer deaths averted, she said.
However the recommendation for screening at a younger age was criticised by some gastroenterology researchers who said it would divert limited colonoscopy resources away from older people who had a much higher absolute risk of colorectal cancer.
Professor Robert Schoen, Chief of the Division of Gastroenterology, Hepatology and Nutrition at the University of Pittsburgh, said the ACS recommendation would see “young kale-eating runners” insisting on getting screening for colorectal cancer despite their low absolute risk of the condition.
He noted that colorectal cancer incidence rates were around 19-33 per 100,000 people in the 40-50 age group compared to incidence rates of 142-247/100,000 in people over 70.
It did not make sense to switch the focus on to young people when screening rates were still much less than optimal among older people with a much high rates of disease, he said.
“We should focus our efforts on groups more likely to benefit; adding lower risk folks will dilute the number who benefit overall,” said Professor Schoen.
There were also unanswered questions about whether younger onset cancers followed the same progression as colorectal cancers in older people, he said, and also whether screening would be as effective in mitigating risk in younger people.