Colorectal cancer screening is now recommended at age 45 years for average-risk individuals; however, optimal outreach strategies to screen younger adults are unknown. Authors aim to determine the most effective population health outreach strategy to promote colorectal cancer screening in adults aged 45 to 49 years. In a randomized clinical trial, 20,509 participants used 4 types of colorectal cancer screening: (1) fecal immunochemical test (FIT)–only active choice; (2) colonoscopy-only active choice; (3) dual-modality (FIT or colonoscopy) active choice; and (4) usual care default mailed FIT outreach.

Findings: The 3 strategies requiring active choice through the electronic patient portal were significantly less effective than default unsolicited mailed fecal immunochemical test (FIT) outreach: 16.4%, 14.5%, and 17.4% vs. 26.2%. Overall screening rates were low, underscoring the need for more effective strategies to engage this age group.