- This large, prospective cohort study of 111,801 U.S. women, followed for more than 26 years in the Nurses' Health Study II, evaluated associations between the risk of colorectal cancer (CRC) and the age of initiating screening endoscopy
- Initiation of endoscopy before age 50 was associated with a reduced risk of CRC, including the risk of CRC diagnosed before age 55
- Earlier initiation of endoscopy was associated with a greater absolute risk reduction of CRC compared with initiation at later ages
- There was no association between CRC mortality and initiation of endoscopy before age 50
- These results support recent national guidelines that recommend starting CRC screening at age 45 for average-risk individuals
The overall incidence of colorectal cancer (CRC) in the U.S. has decreased in recent decades, but it's rising steadily among people under 50. The American Cancer Society and the U.S. Preventive Services Task Force now recommend starting screening at age 45 for individuals at average risk. However, this guidance is based on the results of computer modeling.
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Massachusetts General Hospital researchers addressed this knowledge gap using data from the Nurses' Health Study II. In JAMA Oncology, they linked initiation of endoscopy before age 50 with reduced risk of CRC, including the risk of CRC diagnosed before age 55.
The authors are Mingyang Song, MD, ScD, a researcher in the Clinical and Translational Epidemiology Unit and Division of Gastroenterology at Massachusetts General Hospital, and assistant professor of Medicine at Harvard Medical School, Andrew T. Chan, MD, MPH, chief of the Clinical and Translational Epidemiology Unit and vice chief for clinical research in the Division of Gastroenterology, director of Cancer Epidemiology at the Mass General Cancer Center, and professor of Medicine at Harvard Medical School, Wenjie Ma, MBBS, ScD, instructor and investigator in the Clinical and Translational Epidemiology Unit, assistant in Epidemiology in the Division of Gastroenterology, and instructor in Medicine, Harvard Medical School, and colleagues.
The Nurses' Health Study II began in 1989 by enrolling 116,429 female registered nurses ages 24 to 44 years old. Every two years, participants completed questionnaires about demographics, medical history, and lifestyle factors.
Questions about endoscopy were first asked in 1991, when the participants were 26 to 46 years old. The current analysis included 111,801 participants who were followed from 1991 to 2017. The data were analyzed between August 2020 and June 2021.
Overall CRC Incidence
The primary endpoint was overall CRC incidence. In a multivariable analysis, compared with no endoscopy, screening endoscopy was associated with a significantly lower risk of incident CRC:
- Endoscopy initiated before age 45—HR, 0.37 (95% CI, 0.26–0.53)
- Initiated at age 45 to 49 years—HR, 0.43 (95% CI, 0.29–0.62)
- Initiated at age 50 to 54 years—HR, 0.47 (95% CI, 0.35–0.62)
- Initiated at age 55 years or older—HR, 0.46 (95% CI, 0.30–0.69)
Absolute Risk Reduction
Starting screening at age 45 to 49 was associated with a greater reduction in the absolute risk of CRC compared with starting screening at age 50 to 54. Specifically, the reduction in the cumulative incidence of CRC was 72 per 100,000 persons from age 33 (the lowest age in the analysis) through 60.
Incidence of Younger-onset CRC
Initiation of endoscopy was associated with a lower risk of younger-onset CRC (diagnosed before age 55). Compared with no endoscopy:
- Endoscopy initiated before age 45—HR, 0.45 (95% CI, 0.29–0.70)
- Initiated at age 45 to 49 years—HR, 0.43 (95% CI, 0.24–0.76)
- Initiated at age 50 to 54 years—HR, 0.50 (95% CI, 0.27–0.92)
The risk of CRC mortality was reduced when screening was initiated at age ≥50 but not when it started before age 50. However, the power for the latter analysis was limited because there were only eight deaths from CRC in the younger group.
These results support the guidelines that recommend starting CRC screening at age 45. Patients, physicians, and policymakers now have empirical evidence to consider when making decisions about CRC screening at younger ages.
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