The incidence of colon and rectal cancer in adults younger than 50 years has increased substantially over the latest available 10-year period in several high-income countries, going against a decline or stabilisation trend in the incidence of colorectal cancers within the overall populations of high-income countries.
This is according to an observational study published in The Lancet Gastroenterology & Hepatology journal, which looked at long-term data for colon and rectal cancer incidence in 21 population-based registries across Australia (1983-2012), Canada (1995-2014), Denmark (1978-2012), Ireland (1995-2013), New Zealand (1995-2014), Norway (1953-2014), and the UK (1995-2014).
During the most recent 10-year period up until 2014, the incidence of colon cancer in people aged 0-49 years increased significantly each year in Denmark (by 3.1%), New Zealand (2.9%), Australia (2.9%), and the UK (1.8%). Significant increases in the incidence of rectal cancer each year were also noted in this age group in Canada (by 3.4%), Australia (2.6%), and the UK (1.4%). Increases in the incidence among adults under 50 were most pronounced for rectal cancer, particularly in the 20-29 age group, where rectal cancer incidence increased annually by 18.1% in Denmark and 10.6% in Norway over the past decade.
Across the same time period, significant decreases in incidence of colon cancer per annum were observed in those aged over 50 in Australia (by 1.6%), Canada (1.9%), and New Zealand (3.4%) and of rectal cancer in Australia (2.4%), Canada (1.2%), and the UK (1.2%). Colorectal cancer is the third most common cancer worldwide, with an estimated 1·8 million new cases diagnosed and 881,000 deaths associated with the disease in 2018. This study is the first of its kind to comprehensively address and compare age-specific trends in the incidence of colorectal cancer, with its findings identifying divergent trends for different age groups.
Although the incidence of colorectal cancer in adults younger than 50 years remains much lower compared with that in older age groups, our findings are of concern and highlight the need for action to counteract the rising burden of the disease in younger people. This rise in incidence among younger generations is likely to be driven in part by the changing prevalence of risk factors, such as obesity and poor diet. National programmes to promote healthy diets and physical activity might be the most efficient approach to ensure population-level changes, says the lead author of the study, Dr Marzieh Araghi from International Agency for Research on Cancer, Lyon.
The authors of the study suggest that the decrease in incidence of colorectal cancer in people over 50 years old in most of the countries studied could be attributed to the introduction of routine screening programmes for premalignant polyps. In Australia, Canada, and the UK, where age-based screening began in 2006, overall decreases in incidence were more pronounced. In those countries where screening programmes began later, such as in Ireland (2012), Denmark (2014), Norway (2012, pilot programme only), and New Zealand (2017), overall rates have remained roughly stable.
Dr Araghi adds, 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. However, future studies are needed to establish the root causes of this rising incidence to enable the development of effective preventive and early-detection strategies.
In terms of limitations, the researchers did not have access to individual-level data on risk factors and screening, so could not examine how changes to these factors interacted with trends in colorectal cancer over time. Furthermore, as noted in the linked commentary, there were only seven high-income countries included in this study; adding data from more countries could strengthen the conclusions on the changing epidemiology of colorectal cancer.
Writing in a linked commentary, Professor Giulia Martina Cavestro from Vita-Salute San Raffaele University, Milan says, Araghi and colleagues address the debate about lowering the age of screening. In 2018, the American Cancer Society recommended that screening for colorectal cancer should start at age 45 years for all adults. Such an approach is needed, but other initiatives should be endorsed alongside this decision.
Furthermore, public awareness campaigns are essential to increase adherence to screening, and more gastroenterology units are likely to be needed. The lower age for screening should not be one-size-fits-all — personal and family history should be taken into account. Among the many risk factors, the importance of taking an accurate family history during a risk assessment cannot be overstated.
The new research also reveals that the rate of bowel cancer otherwise known as colorectal cancer or CRC is rising among adults aged 20-49 in Europe. Rates rose most steeply among the youngest age group (20-29 years), and the authors warn that if the trend continues, screening guidelines may need to be reconsidered. Rates tend to be lower among people over 50, but the opposite is true among younger adults in North America, Australia and China, say the researchers. And in the US, the increase in new cases among people aged 20-40 has prompted
The American Cancer Society to recommend lowering the age at which to start screening to 45.
Over the past decade, the number of new cases of bowel cancer has risen in most European countries, but the situation on rates among younger adults is unclear.
So to shed some light on European trends, a team of researchers analysed data from national and regional cancer registries on the number of new cases and deaths related to bowel cancer between 1990 and 2016. They used data from 143.7 million people aged 20-49 years from 20 countries, including Germany, Sweden, the UK and the Netherlands.
Between 1990 and 2016, a total of 187,918 people were diagnosed with bowel cancer and there was a steeper rise in the number of new cases in more recent years. Among 20-29 year olds, bowel cancer incidence rose from 0.8 to 2.3 cases per 100,000 people between 1990 and 2016, and the sharpest rise was between 2004 and 2016 at 7.9% per year. For the 30-39 year olds group, the incidence increased less steeply than the younger age group, at an average of 4.9% per year from 2005 to 2016.
Finally, among the 40-49 years age group, the bowel cancer rates fell by 0.8% between 1990-2004, but then increased slightly by 1.6% per year from 2004 to 2016. New cases of bowel cancer rose significantly among people aged 20-39 in 12 countries, namely, Belgium, Germany, the Netherlands, the UK, Norway, Sweden, Finland, Ireland, France, Denmark, Czech Republic and Poland. But Italy showed a decrease in the number of cases.
In eight countries — the UK, Greenland, Sweden, Slovenia, Germany, Finland, Denmark and the Netherlands — the number of cases rose significantly among 40-49 year olds, but rates fell significantly in the Czech Republic in more recent years (1997-2015). The number of deaths from bowel cancer did not significantly change among the youngest adults (20-29 years), but fell by 1.1% per year between 1990 and 2016 in the 30-39 age group and by 2.4% per year between 1990 and 2009 among those aged 40-49 years.
This is an observational study, and as such, cannot establish cause. Moreover, the authors highlight some limitations, including the fact that the quality of data varied between countries and in some cases was only available for a limited number of regions. Several factors may be behind these trends, including the rise in obesity, and lifestyle factors such as lack of physical activity, alcohol intake and smoking, they write. Bowel cancer in young adults is in part due to hereditary cancer syndromes, but most cases are sporadic, they add.