A multicentre randomized health services study within the population-based primary colonoscopy screening program (PCSP) in Poland. Individuals, aged 55-60 years, willl be randomized in a 1:1:1 ratio to arms: (1) Invitation by post, (2) Call Center or (2) Combined invitation methods. The primary outcome measure is rate of participation in screening colonoscopy. The sample size of 6 300 participants will detect 3 to 5 percentage point differences (depending on the arms comparison) in participation rate between groups with 80% power and significance level 0.05, using Ochran-Mantel-Haenszel test.

This randomized health services study will be performed within national population-based screening program (PCSP) in Poland, including its population, infrastructure and database system.

Individuals aged 55-64 years old, included in PCSP willl be randomly assigned (in 1:1:1 ratio, stratified by gender, age, place of residence) to study arms and invited to screening colonoscopy to local PSCP centers.

Invitation process by post in Control group (1) and partially in Combined group (3) - will be performed by coordinating PCSP center (practice as usual).

Recruitment by telephone conversation in Call Center group (2) and partially in Combined group (3) - will be performed by Screening Up call center company. Colonoscopies will be performed in 6 selected PCSP centers.

The sample size of 2,100 participants per group (350 participants from each group in each center, assuming 5% drop out and access to telephone numbers of 30% participants in relevant arms; calculation is based on a 95% confidence interval +/- 5% error probability) was calculated to detect a difference in participation rate of 15% in control group (based on PCSP participation rate in 2019) vs. 18.7% in Call Center group vs 25% in Combined Invitation group (0.025 significance level with 80% power). The difference was calculated for the Cochran-Mantel-Haenszel test, assuming that the initial reporting in the control group will be as high as it was in 2019.

Differences in participation rate to screening colonoscopy between the study groups and the control group will be performed using Ochran-Mantel-Haenszel test (two-sided analysis), taking into account initial differences between rates at the significance level of 0.05.

The Principal Investigator of the study asked the Bioethical Committee with a request to release participants from signing of informed consent form to participation in the study, as they take part in a nationwide PSCP, financed by Ministry of Health in Poland - the study character is the Randomized Health Services Study.

Inclusion Criteria:

• population included to invitation within Polish population based Colorectal cancer Screening Program (PCSP)

  • 55-64 of age
  • no history of CRC
  • no history of screening colonoscopy within PCSP

• adress of residence near (not further than 40 kilometers) local PCSP centers (selected for the study based on population density)

Exclusion Criteria:

• none