Age at Initiation of Colorectal Cancer Screening and Risk of Colorectal Cancer Among U.S. Women

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In a study reported in JAMA Oncology, Ma et al found that the initiation of lower gastrointestinal endoscopy screening in women younger than age 50 was associated with a reduced risk of colorectal cancer vs no screening, and a greater absolute risk reduction compared with screening starting at age 50 or later.

As stated by the investigators, “In the past 4 years, the American Cancer Society and the U.S. Preventive Services Task Force updated recommendations to initiate colorectal cancer screening at 45 years of age to address the increasing incidence of colorectal cancer among adults younger than 50 years. However, empirical evidence evaluating the potential benefits of screening in younger populations is scant.”

Study Details

The prospective cohort study used data from the Nurses’ Health Study II, which included U.S. female health professionals followed up from 1991 through 2017. Data analysis was performed from August 2020 to June 2021.

Data included age at initiation of sigmoidoscopy or colonoscopy for routine screening, screening due to family history, or to assess symptoms. The cumulative incidence of colorectal cancer in age groups was estimated and the absolute risk reduction associated with endoscopy initiation in age groups through 60 years was calculated.

Key Findings

Among 111,801 women aged 26 to 46 years (median = 36 years) at enrollment included in the analysis, 519 incident colorectal cancer cases were documented over 26 years, representing a total of 2,509,358 person-years of follow-up.

On multivariate analysis, compared with no endoscopy, undergoing endoscopy was associated with a significantly lower risk of incident colorectal cancer for age at initiation at < 45 years (hazard ratio [HR] = 0.37, 95% confidence interval [CI] = 0.26–0.53), 45 to 49 years (HR = 0.43, 95% CI = 0.29–0.62), 50 to 54 years (HR = 0.47, 95% CI = 0.35–0.62), and ≥ 55 years (HR = 0.46, 95% CI = 0.30–0.69).

Compared with no endoscopy, the estimated reduction in incident colorectal cancer cases per 100,000 persons from age 33 to 60 years was 435 (64%) among those who initiated screening before 45 years of age, 356 (52%) for initiation at 45 to 49 years, 284 (41%) for initiation at 50 to 54 years, and 153 (22%) for initiation at ≥ 55 years. This represents a reduction in the cumulative incidence of colorectal cancer of 72 per 100,000 persons through age 60 years for endoscopy initiation at 45 to 49 years vs 50 to 54 years.

A total of 299 cases of colorectal cancer were documented with onset before age 55. Compared with no endoscopy, initiation of endoscopy at age < 50 years was associated with reduced risk of colorectal cancer diagnosed before age 55 years, with hazard ratios of 0.45 (95% CI = 0.29–0.70) for initiation at age < 45 years and 0.43 (95% CI = 0.24–0.76) for initiation at age 45 to 49 years. 

The investigators concluded, “In this cohort study, compared with no endoscopy, initiation of endoscopy before 50 years of age was associated with a reduced risk of colorectal cancer, including colorectal cancer diagnosed before 55 years of age. Screening before 50 years of age was associated with greater absolute reduction in colorectal cancer risk compared with initiation of colorectal cancer screening at 50 years of age or later.”

Mingyang Song, MD, ScD, of the Department of Epidemiology, Harvard T.H. Chan School of Public Health, and Andrew T. Chan, MD, MPH, of the Clinical and Translational Epidemiology Unit, Massachusetts General Hospital, are the corresponding authors for the JAMA Oncology article.

Disclosure: The study was supported by grants from the National Institutes of Health. For full disclosures of the study authors, visit