Participation in a primary screening colonoscopy programs remains low. Advanced notification letter has been shown to increase participation in colorectal cancer screening with fecal occult blood testing and to be cost effective compared to standard invitation. It is unknown whether advanced notification letter increases participation rate in primary colonoscopy screening program.

We hypothesize that an Advance Notification Letter will have significant influence on participation in screening colonoscopy, comparing to standard invitation procedure and will thus result in higher efficiency of the program.

This randomized controlled study aims to compare the participation rate in screening colonoscopy in response to advanced notification plus standard invitation letter and standard invitation letter alone.

Material and methods: 6800 individuals aged 55-64 years will be drawn from the Population Registry and randomly assigned in a 1:1 ratio to the group invited for screening colonoscopy with advanced notification letter (send two weeks before standard invitation) plus standard invitation (send six weeks before planned screening colonoscopy) or to standard invitation only (send six weeks before planned screening colonoscopy). The sample size was calculated to detect 3% difference in participation rate between the groups (25% vs 28%) with 80% power.

Inclusion Criteria:

• all individuals aged 55-64 years living in the counties covered with the organized CRC screening program and assigned to invitation to screening colonoscopy in the year 2014 are eligible for the study.

Exclusion Criteria:

• message from neighbor/family/post office on death of screenee (not updated in Population Registry)
• resident abroad (not updated in Population Registry)
• return of unopened letter of invitation and/or reminder (address unknown)
• diagnosis of CRC before the date of draw (not updated in the National Cancer Registry)