Colonoscopy and sigmoidoscopy provide protection against colorectal cancer, but the magnitude and duration of protection, particularly against cancer of the proximal colon, remain uncertain.
Dr Reiko Nishihara and colleagues examined the association of the use of lower endoscopy with colorectal-cancer incidence, and colorectal-cancer mortality among participants in the Nurses' Health Study and the Health Professionals Follow-up Study.
Among 88,902 participants followed over a period of 22 years, the researchers documented 1815 incident colorectal cancers and 474 deaths from colorectal cancer.
With endoscopy as compared with no endoscopy, multivariate hazard ratios for colorectal cancer were 0.57 after polypectomy, 0.60 after negative sigmoidoscopy, and 0.44 after negative colonoscopy.
|The hazard ratio for death from colorectal cancer was 0.59 after screening sigmoidoscopy|
|New England Journal of Medicine|
The researchers found that negative colonoscopy was associated with a reduced incidence of proximal colon cancer.
Multivariate hazard ratios for death from colorectal cancer were 0.59 after screening sigmoidoscopy, and 0.32 after screening colonoscopy.
The team observed reduced mortality from proximal colon cancer after screening colonoscopy but not after sigmoidoscopy.
As compared with colorectal cancers diagnosed in patients more than 5 years after colonoscopy or without any prior endoscopy, those diagnosed in patients within 5 years after colonoscopy were more likely to be characterized by the CpG island methylator phenotype (CIMP), and microsatellite instability.
Dr Nishihara's team concludes, "Colonoscopy and sigmoidoscopy were associated with a reduced incidence of cancer of the distal colorectum."
"Colonoscopy was also associated with a modest reduction in the incidence of proximal colon cancer."
"Screening colonoscopy and sigmoidoscopy were associated with reduced colorectal-cancer mortality."
"Only colonoscopy was associated with reduced mortality from proximal colon cancer."
"Colorectal cancer diagnosed within 5 years after colonoscopy was more likely than cancer diagnosed after that period or without prior endoscopy to have CIMP and microsatellite instability."