HONOLULU — Roughly 2%–4% of newly diagnosed colon cancers in a busy private gastroenterology practice were missed at colonoscopy performed within the prior 36 months, John F. Johanson, M.D., said at the annual meeting of the American College of Gastroenterology.
“The implication of these data is that even in experienced hands, colonoscopy is not perfect. We all understand that. But I think it needs to be communicated to our patients. We've now actually incorporated the possibility of a missed lesion into our informed consent,” said Dr. Johanson, a Rockford, Ill., gastroenterologist.
The data will also be used to develop benchmarks for quality assurance efforts.
Dr. Johanson reviewed computerized medical records for 2003 and 2004 in a private practice with 12 board-certified gastroenterologists. Each had performed at least 2,000 colonoscopies, and most had done far more than 5,000. During the study period they did 16,147 colonoscopies, leading to detection of cancer in 204 patients. Thus, 1 in 80 procedures resulted in diagnosis of colon cancer.
Eight patients had colonoscopy within 36 months prior to diagnosis. Malignant transformation of polyps is typically a slow process, so the initial assumption was that all these were missed lesions. This yielded a missed cancer rate—or as Dr. Johanson prefers to call it, a “surprise” colon cancer rate of 3.9%. There were two T-4 lesions, four T-3s, one T-2, and one T-1. They did not cluster by location or colonoscopist.
Upon examination of the detailed records of the prior colonoscopies, it became apparent that two of the eight colon cancers weren't truly missed, thus dropping the miss rate to 2.9%.
One such patient had a large rectosigmoid polyp removed and came back for another colonoscopy 1 year later, when it was found the polyp had returned. It was removed again down to the base. When the patient came back again a year later, the lesion had returned—and was now malignant.
Another patient, referred for evaluation of abdominal pain, had an incomplete colonoscopy due to technical reasons; the scope could be advanced only to the midtransverse colon. A year and a half later the patient was back, this time with rectal bleeding—and cancer of the ascending colon.
Two other patients had cancers in the same locations as adenomas that, in hindsight, were probably incompletely removed. In the remaining four patients, there was no clear explanation for the surprise colon cancer. Dr. Johanson's study received a 2005 ACG/Olympus Award.