Context: The recommended interval for colorectal cancer screening with flexible sigmoidoscopy (FS) was recently lengthened from 3 to 5 yr. Direct evidence supporting the longer interval is lacking. The appropriateness of the longer interval has been questioned.
Objective: To compare the incidence of neoplasia detected on FS in individuals who had undergone an FS either 3 yr or 5 yr after a normal examination.
Design, settings, and patients: Subjects were drawn from 5,359 individuals who underwent two FS examinations performed for colorectal cancer screening. Examinations were performed by gastroenterologists at a single academic medical center between 1987 and 2002. A total of 2,146 subjects with a normal baseline examination and a follow-up examination 3 and 5 yr later was included.
Main outcome measure: To compare the incidence of neoplasia, including advanced neoplasia, detected 3 yr versus 5 yr after a normal FS.
Results: 915 subjects underwent FS at 3 yr and 1,231 subjects at 5 yr after a normal examination. Neoplasia was detected in 3.2% of the 3-yr and 4.3% of the 5-yr subjects (p=0.17). No significant differences were detected in the pathology, multiplicity, or size of neoplasms between the 3- and 5-yr groups. Advanced neoplasms occurred in 0.9% (including one adenocarcinoma) of subjects at 3 yr and 1.1% of subjects at 5 yr (p=0.67).
Conclusions: Few individuals will develop rectosigmoid neoplasms 3 or 5 yr after a normal FS. The majority of neoplasms detected are low-risk lesions. A screening interval of 5 yr after a normal FS does not portend an increased risk of advanced neoplasms including cancer. This direct evidence supports the current recommendations of a 5-yr interval for colorectal cancer screening with FS.