Colorectal cancer illustration showing a view from inside the intestine

Research led by the Karolinska Institute in Sweden confirms that early testing for unseen blood in a person’s stool reduces deaths from colorectal cancer by 14%.

“Secondary prevention of colorectal cancer with screening has the potential to reduce deaths from the disease by detecting the cancer at an early, curable stage. Larger precursors, such as adenomatous polyps (adenomas), and cancer may bleed, enabling the measurement of invisible (occult) blood in the stool with fecal occult blood tests before disease symptoms occur,” explained Johannes Blom, a researcher at the Karolinska Institute, and co-authors in JAMA Network Open.

Some form of colorectal cancer screening with fecal occult blood tests has been recommended in many countries for the last decade, but data on the effectiveness of this screening on reducing cancer deaths in large scale community populations is lacking.

The current study included 379,448 individuals living in the region of Stockholm-Gotland in Sweden. All residents born between 1938 and 1954 were invited for colorectal cancer screening using fecal occult blood testing between 2008 and 2021.

The cohort was divided into those invited “early” between 2008 and 2012 (203,670 people) and those invited “late” (between 2013 and 2015) or not at all (175,778 people). Results from the early group were compared with the late or zero testing group, which acted as a control group.

Overall, screening was taken up by 63% of the study population. Over a maximum of 14 years of follow-up, 834 people died of colorectal cancer in the early testing group versus 889 people in the control group.

When uptake of screening was considered, those in the early group had a 14% reduced risk of dying from colorectal cancer compared with those in the control group.

Blom and colleagues believe the actual mortality risk reduction gained from this form of screening may be even higher than the result they achieved in their study.

“Dilution of the estimated effectiveness is expected due to some later screening in the control group and some colorectal cancer deaths occurring among individuals who received a diagnosis years after invitations to screening had ended,” wrote the authors.

“Our results have an important public health implication in suggesting that organized population-based colorectal cancer screening with fecal occult blood tests has the potential to save lives worldwide.”

The team adds that since fecal occult blood tests were first introduced, a more accurate version of this test known as fecal immunochemical testing, or FIT, has been introduced. FIT has a higher sensitivity and adherence rate than guaiac-based fecal occult blood tests.

“By using FIT as screening test… more lives could be saved, but adherence to prompt follow-up colonoscopies after a positive test result is essential,” concluded Blom and colleagues.

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