2010-04-23 18:12:32 UTC

Post-Colonoscopy Colorectal Cancer: Does Endoscopist Specialty Matter?

April 23, 2010

Linda Rabeneck, MD, MPH

Linda Rabeneck, MD, MPH

Professor of Medicine, University of Toronto, Ontario, Canada  


Colonoscopy is the gold standard for detecting colorectal neoplasia, and colonoscopic polypectomy is associated with a reduced incidence of colorectal cancer (CRC).1 Further, two large population-based studies from Manitoba and Ontario have reported that the risk of incident CRC following a negative colonoscopy was reduced for at least 10 years compared with the general population.2, 3 However, we know that a small but clinically meaningful number of incident CRCs are diagnosed following a colonoscopy in which the cancer was not detected. Several factors might explain these unwelcome events, including missed lesions due to poor bowel preparation, suboptimal colonoscopy technique, incomplete polypectomy and new CRCs that may arise following a truly negative colonoscopy.


It is often not possible to be certain that a CRC that was not detected at the time of colonoscopy, but is subsequently diagnosed, was a missed cancer. The alternative explanation is that the “new” cancer was not present at the time of the colonoscopy, but is truly new, and arose and grew rapidly following the procedure. For this reason, we recommend and use the term post-colonoscopy CRC (PCCRC) in reference to CRC identified after a prior colonoscopy.4

A key advantage of the term PCCRC is that it does not imply or assume whether the cancer was new or missed, as most often this is unknown and cannot be discovered. In addition, the associated time period in which the PCCRC is diagnosed following the colonoscopy (e.g., one year, three years, five years) can be specified to facilitate comparisons across studies. For example, this could be denoted as PCCRC (one year). Further, the term PCCRC can be used regardless of the specific indication for the colonoscopy to facilitate comparisons relative to that specific indication. We prefer PCCRC to “interval cancer,” as the latter refers to cancers that occur following a negative screening episode — in this case, screening colonoscopy — in the interval before the next screen is due.5

Recent findings

In the March 2010 issue of Clinical Gastroenterology and Hepatology, we reported our findings from a study that investigated whether endoscopist specialty is associated with PCCRC following a negative complete colonoscopy.6 We identified a cohort of 110,402 individuals, 50 to 80 years old who had undergone a negative complete colonoscopy; the majority (86 percent) had their procedures performed in hospitals. During the 15-year follow-up period, 1,596 (14.5 percent) were diagnosed with PCCRC. Among those 86 percent of persons who had their colonoscopies at a hospital, those who had their procedures performed by a non-gastroenterologist were at significantly increased risk of PCCRC. For those who had their colonoscopies in a private office/clinic, endoscopist specialty was not significantly associated with PCCRC. In the private office/clinic, a relatively small proportion of colonoscopies (8 percent) was done by gastroenterologists, so we may not have been able to detect an association.

How does this square with previous findings on PCCRC?

Few studies have evaluated factors associated with PCCRC following negative colonoscopy. Because this outcome is relatively uncommon, a large study cohort is required. The Manitoba study reported a non-significant trend towards general practitioners performing a higher proportion of the colonoscopies in persons with a PCCRC following a negative colonoscopy.2 In an earlier, separate, population-based study of 12,487 persons with a new diagnosis of CRC who had a colonoscopy within the three years before their diagnosis, we reported that, compared with having the colonoscopy performed by a gastroenter-ologist, having the procedure performed by an internist or family physician was independently associated with PCCRC.7 A U.S. study conducted at 20 Indiana hospitals reported that in 47 (5 percent) of 941 patients with CRC, the cancer was missed at colonoscopy and the risk of missed CRC was greater for non-gastroenterologists compared with gastroenterologists.8

Colonoscopy: quality is imperative

It is important that the practice of colonoscopy is skilled and effective. We now have clear evidence that endoscopist specialty matters and is an important determinant of the effectiveness of colonoscopy in usual clinical practice. Overall, gastroenterologists are more proficient at colonoscopy than others, including general surgeons. This may reflect the considerable formal training in endoscopy that forms part of gastroenterology core training requirements in the U.S. and Canada. As gastroenterologists, we need to continue to lead in colonoscopy training and in setting evidence-based standards for colonoscopy quality. We also need to embrace and participate in colonoscopy performance measurement and reporting in our own practices so that we can show, by example, how best to provide and enhance these crucial services. 


  1. Winawer SJ, Zauber AG, Ho MN, et al. Prevention of colorectal cancer by colonoscopic polypectomy. N Engl J Med 1993;329:1977-81.
  2. Singh H, Turner D, Xue L, et al. Risk of developing colorectal cancer following a negative colonoscopy examination: evidence for a 10-year interval between colonoscopies. JAMA 2006;295:2366-73.
  3. Lakoff J, Paszat LF, Saskin R, et al. Risk of developing proximal versus distal colorectal cancer after a negative colonoscopy: A population-based study. Clin Gastroenterol Hepatol 2008;6:1117-21.
  4. Rabeneck L, Paszat LF. Circumstances in which colonoscopy misses cancer. Frontline Gastroenterology 2010; in press.
  5. Moss S, Ancelle-Park R, Brenner H. Evaluation and interpretation of screening outcomes. In: European Guidelines for Quality Assurance in Colorectal Cancer Screening. Eds: Patnick J, Segnan N, von Karsa L. International Agency for Research on Cancer; 2010; in press.
  6. Rabeneck L, Paszat LF, Saskin R. Endoscopist specialty is associated with incident colorectal cancer after a negative colonoscopy. Clin Gastroenterol Hepatol 2010; 8; 275-279.
  7. Bressler B, Paszat LF, Chen Z, et al. Rates of new or missed colorectal cancers after colonoscopy and their risk factors: A population based analysis. Gastroenterology 2007;132:96-102.
  8. Rex DK, Rahmani EY, Haseman JH, et al. Relative sensitivity of colonoscopy and barium enema for detection of colorectal cancer in clinical practice. Gastroenterology 1997;112:17-23.

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