When to Begin Colorectal Cancer Screening in Average-Risk Adults
A 45-year-old woman with no risk factors or family history should begin colorectal cancer screening now. 1, 2
Recommended Starting Age
The American Cancer Society (ACS) recommends that average-risk adults begin colorectal cancer screening at age 45 years, based on microsimulation modeling showing that starting at age 45 versus age 50 provides 6.2% more life-years gained per 1000 screened individuals. 1
The US Preventive Services Task Force (USPSTF) provides a Grade B recommendation for screening ages 45-49 years and a Grade A recommendation for ages 50-75 years, with modeling demonstrating that lowering the start age from 50 to 45 years yields 22-27 additional life-years gained per 1000 persons. 2, 3
This recommendation is driven by rising colorectal cancer incidence in younger adults due to a birth-cohort effect beginning in the 1950s, with adults born circa 1990 having approximately 2.4 times higher risk of colon cancer and 4 times higher risk of rectal cancer compared to earlier cohorts. 1
First-Tier Screening Options
Colonoscopy every 10 years is the preferred initial screening modality because it combines detection and immediate therapeutic intervention in a single procedure. 2, 4
Annual fecal immunochemical testing (FIT) is an equally acceptable first-tier alternative when patient adherence is high, particularly in organized screening programs. 2, 4
When screening from ages 45-75 years, colonoscopy every 10 years provides 429 life-years gained per 1000 screened, compared to 403 life-years gained with annual FIT. 1
Alternative Screening Modalities
If colonoscopy is declined, offer these second-tier options:
CT colonography every 5 years (390 life-years gained per 1000 screened from ages 45-75). 1
Flexible sigmoidoscopy every 5 years (403 life-years gained per 1000 screened from ages 45-75). 1
Multi-target stool DNA testing every 3 years (376 life-years gained per 1000 screened from ages 45-75). 1
Critical Implementation Points
The recommendation to start at age 45 carries moderate certainty (Grade B) compared to high certainty (Grade A) for ages 50-75, reflecting emerging rather than decades-long evidence. 2
Starting screening at age 45 requires 17% more colonoscopies over a lifetime compared to starting at age 50 (5,646 versus 4,836 colonoscopies per 1000 screened), but this burden is justified by the additional life-years gained. 1
Any positive result from a non-colonoscopy screening test must be followed by diagnostic colonoscopy to complete the screening pathway. 2
Tests to Avoid
Guaiac-based fecal occult blood testing performed on digital rectal exam specimens should not be used due to very low sensitivity. 2
Septin9 serum testing is not recommended for routine screening due to insufficient evidence of effectiveness. 2, 4