People who take part in screening for colorectal cancer may have as much as 43 per cent lower risk of dying from the disease, according to new estimates published in JAMA Network Open by researchers at Karolinska Institutet and Umeå University in Sweden. These findings are based on up to 14 years of follow-up data from the Stockholm–Gotland screening programme.

Colorectal cancer is one of the most common forms of cancer, with a favourable prognosis if detected early. Universal screening has been introduced throughout Sweden, meaning testing is offered to people aged 60–74 every two years. Participants are sent a screening kit to their home address and asked to provide a stool sample, which is analysed for small amounts of blood that are not visible to the naked eye. If blood is detected, further investigation is offered, usually in the form of a colonoscopy.

New study shows greater effectiveness

Stockholm and Gotland were early adopters, introducing routine screening as early as 2008. Researchers at Karolinska Institutet and Umeå University have now followed these individuals for up to 14 years to investigate the impact of screening on mortality rates.

“A previous evaluation of the programme showed that those who received an invitation to screening had a 14 per cent lower risk of dying from the disease,” says Johannes Blom, senior consultant and associate professor at the Department of Clinical Science and Education, Södersjukhuset, Karolinska Institutet, and the study’s corresponding author. “We have now been able to show that the mortality is significantly lower than that among those who actually take part in the screening.”

One-third do not take part in screening

The researchers compared those who were invited to screening between 2008 and 2012 with a control group who were either invited later or not at all. They used a statistical method to account for factors that could distort the results, such as some people in the control group being given the opportunity to participate later on, and some invited individuals not participating.

When these factors were taken into account, an invitation to screening was associated with a 26 per cent lower risk of dying from colorectal cancer, while active participation was associated with a 43 per cent lower risk.

“Although screening is offered free of charge and the test is simple to carry out, around a third of people do not submit a sample,” says Johannes Blom. “Our study highlights the importance of taking part in colorectal cancer screening, and shows that it can actually save lives.”

Over 376,000 study participants

The study included 376,511 people, and during the follow-up period, 1,668 deaths from colorectal cancer were recorded. Some of the study’s strengths include the large study population, the long follow-up period and the use of Swedish health registers. However, the researchers emphasise that the results are based on statistical adjustments for various types of bias, meaning that some uncertainties remain.

The study was funded by the Swedish Cancer Society, the Swedish Research Council and Region Stockholm. The researchers state that they have no conflicts of interest.