Colorectal cancer (CRC) is the third leading cause of cancer mortality in Switzerland, and kills 1600 people annually. Most deaths could be prevented by screening, but the 2012 Swiss national health survey found that only 40% of 50-75-year-olds had been tested within recommended intervals (26% with colonoscopy in the last 10 year, 7% with fecal occult blood test [FOBT] in the last 2 years, and 7% with both). If screening starts at age 50, in the average risk population absolute risk of dying from CRC at age 80 can be cut from 2% to 1%, reducing relative risk by 50%. Since 2013, Switzerland has reimbursed screening by colonoscopy every 10 years or FOBT every 2 years for adults 50-69 years old. Conforming to current recommendations, the Federal Office of Public Health (FOPH) officially recognizes both screening modalities.

When patients are offered a choice of screening test (colonoscopy vs. FOBT), they are as likely to opt for one as the other. Patient preferences are unlikely to vary much between PCP practices, so distribution of colonoscopy and FOBT within each practice should also be roughly equal. Family physicians are recognized as the most trusted professional to discuss CRC screening in Switzerland. However, many primary care physicians (PCPs) prefer prescribing colonoscopy over FOBT, but physician preference for method seems to vary widely between regions. If physician preferences and local medical culture currently influence choice of method more strongly than patient preferences, encouraging PCPs to diagnose patient preferences for screening method may reduce the number of PCPs who prescribe only one method. An earlier study in Switzerland showed that training PCPs and giving them educational support and decision aids raised the number who intend to prescribe colonoscopy and FOBT in equal proportions. A randomized controlled trial in the US showed that when patients were offered both FOBT and colonoscopy rather than only colonoscopy alone, more patients were screened for CRC. Offering choice of method may thus increase overall screening rates.

The Swiss Sentinel Surveillance Network (Sentinella) is a cooperative surveillance project including the Federal Office of Public Health (FOPH), PCPs representatives and the five Swiss institutes of family medicine. A sample of 150 to 250 general practitioners, internists and pediatricians in private practices from all regions of Switzerland report weekly morbidity data to the network using irreversibly anonymized patient data collected during consultations. In 2017, 91 out of 129 eligible PCPs of the Sentinella network participated in a cross-sectional data collection on CRC screening. The Sentinella network appears ideally suited to perform an intervention in order to modify screening practices and measure outcomes using the same collection form as in 2017.

This study will test the benefits of a prepackaged training program in participatory medicine sent by post to PCPs in Switzerland. The package is designed to improve their diagnoses of patient preferences for screening and screening method (colonoscopy or FOBT). The study begins with the hypothesis that giving PCPs evidence summaries on CRC screening, decision aids for patients, and performance feedback on the 2017 data collection will increase the number of PCPs whose patients include at least one screened with FOBT, and who will prescribe at least one FOBT/FIT (Fecal Immunochemical Test) instead of prescribing only colonoscopy. This might reduce variation in care between PCP practices by increasing variation in methods of screening prescribed within each PCP practices. Analyses from the 2017 data collection suggest that fewer patients refused CRC testing in practices that offered both methods than in practices that offered only colonoscopy. This intervention might increase screening rates overall, while respecting patient's autonomy to refuse the test and to be prescribed the test they prefer.

The study will compare outcomes among PCPs allocated to the intervention group to those in the control group, and will be measured by collecting anonymous structured patient data on 40 consecutive patients by PCPs and questionnaires filled by PCPs.

The study is designed to fit within the Reach, Effectiveness, Adoption, Implementation and Maintenance (RE-AIM) framework for structuring data collection. RE-AIM ensures that a study's outcomes for future implementation and dissemination works are collected. The RE-AIM criteria will be used to identify the translatability and public health impact of this intervention, and for making clear to future stakeholders the internal and external validity of study results.

Inclusion Criteria:

• Physician-level: PCPs participating in the Swiss Sentinel Surveillance Network (Sentinella) willing to participate in the study
• Patient-level: Each PCP will collect data on 40 consecutive patients aged 50 to 75 years old seen in PCP offices over a 2 weeks to 2 months period. Patients will be included if there is a face-to-face consultation billed for at least 5 minutes at the practice.

Exclusion Criteria:

• None except criteria which do not respect inclusion criteria