Complete colonoscopy rarely misses cancer

The assumption that colonoscopy is highly accurate for detecting colorectal cancer was tested by identifying cancer subsequent to colonoscopy in 2 cohorts of patients in which colonoscopy was reported as normal.

A multicenter endoscopy database was used to identify all reportedly normal colonoscopies. One cohort was assessed 5 years after colonoscopy with the use of a population-based health services-linked database to link patient morbidity, cancer, and mortality data. The second cohort was assessed by identifying patients who had cancer on repeat colonoscopy.

Of 1047 patients with normal colonoscopies followed for 5 years or until death if earlier, 5 cancers (0.5%) were detected. This rate was not significantly different from that predicted by Australian statistics (risk = 1.0%, p > 0.1), but significantly lower compared with that for all patients presenting for colonoscopy during the study period (risk = 5.2%, p < 0.001). In another cohort of 8486 patients with reportedly normal colonoscopies, 496 patients underwent repeat colonoscopies during an average follow-up of 3.1 years; cancer was diagnosed at the subsequent procedure in 3 patients (0.6%).

The high accuracy of colonoscopy is demonstrated by the low risk of harboring an advanced neoplastic lesion after a normal examination.