The effectiveness of screening colonoscopy in average-risk adults is uncertain, particularly for right colon cancer.
Dr Chyke Doubeni and colleagues from Pennsylvania, USA examined the association between screening colonoscopy and risk for incident late-stage colorectal cancer.
The team performed a nested case–control study in 4 U.S. health plans.
The research team enrolled 1039 average-risk adults for at least 5 years in one of the health plans.
Case patients were aged 55 to 85 years on their diagnosis date of stage IIB or higher colorectal cancer during 2006 to 2008.
|34% of control patients had screening sigmoidoscopy|
|Annals of Internal Medicine|
The team selected 1 or 2 control patients for each case patient, matched on birth year, sex, health plan, and prior enrollment duration.
Receipt of colorectal cancer screening 3 months to 10 years before the reference date, ascertained through medical record audits.
Case patients and control patients were compared on receipt of screening colonoscopy or sigmoidoscopy by using conditional logistic regression that accounted for health history, socioeconomic status, and other screening exposures.
In analyses restricted to 471 eligible case patients and their 509 matched control patients, 13 case patients and 46 control patients had undergone screening colonoscopy.
The team noted that this corresponded to an adjusted odds ratio of 0.29 for any late-stage colorectal cancer, 0.36 for right colon cancer, and 0.26 for left colon/rectum cancer.
The research team found that 20% of cases, and 34% of control patients had screening sigmoidoscopy, corresponding to an adjusted odds ratio of 0.50 overall, 0.79 for right colon late-stage cancer, and 0.26 for left colon cancer.
Dr Doubeni's team commented, "Screening with colonoscopy in average-risk persons was associated with reduced risk for diagnosis of incident late-stage colorectal cancer, including right-sided colon cancer."
"For sigmoidoscopy, this association was seen for left colorectal cancer, but the association for right colon late-stage cancer was not statistically significant."