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Can Colonoscopy Reduce the Risk of Colon Cancer and Mortality in Patients With Inflammatory Bowel Disease?
Clinical Gastroenterology and Hepatology 2015;-:1
LETTER TO THE EDITOR Readers are encouraged to write letters to the editor concerning articles that have been published in Clinical Gastroenterology and Hepatology. Short, general comments are also considered, but use of the Letters to the Editor section for publication of original data in preliminary form is not encouraged. Letters should be typewritten and submitted electronically to http://www. editorialmanager.com/cgh.
Can Colonoscopy Reduce the Risk of Colon Cancer and Mortality in Patients With Inflammatory Bowel Disease? Dear Editor: We read with interest the study by Ananthakrishnan et al1 that showed that colonoscopy within 3 years is associated with a lower risk of colon cancer among patients with inflammatory bowel disease.1 This is an extremely important finding and the results of this study reinforce the need to follow current screening guidelines. Assuming that most of the patients in this study underwent standard white-light endoscopy, this study also raises the bar for future studies of contrast-enhanced endoscopy to show a greater reduction in colon cancer incidence than standard white-light colonoscopy, not just increased detection of dysplasia. However, before we fully accept the results of the current study, we ask that the authors clarify a few potential sources of bias that could have made colonoscopy look particularly effective. The authors reported that their exposure variable was completion of a colonoscopy performed in the 3 years before the index date, which was the date of the colon cancer diagnosis for cases and the end of the follow-up period for controls. They excluded colonoscopies performed in the 6 months immediately before the index date among the cases to avoid inclusion of the colonoscopy that led to the colon cancer diagnosis. This logic is sound but potentially creates a bias by allowing controls a 36-month period during which they could have undergone colonoscopy, whereas cases only had a 30-month period. To avoid this bias, the investigators also would need to exclude the same 6-month time period among the controls. The index date for cases (ie, the date of diagnosis of colorectal cancer) is likely the date of a colonoscopy because colonoscopy is the gold standard test for colon cancer diagnosis. In contrast, the index date of controls
was their last visit. Because colonoscopies are recommended in 1- to 3-year intervals, it is possible in the case group that the colonoscopy before diagnosis of colon cancer was immediately before the window for exposure, yet was in the window of exposure for controls because of the choice of index date. For example, if both case and control patients were undergoing a colonoscopy every 4 years, none of the cases vs 75% of controls would appear to have undergone a colonoscopy in the preceding 3 years despite comparable use of colonoscopy. To determine if this led to a biased result, extending the exposure window for both groups may help. Our last concern also relates to the choice of the end of the follow-up period as the index date among the controls. This likely resulted in the index date occurring, on average, in later years among controls than among cases. The use of surveillance colonoscopy has increased over time among patients with inflammatory bowel disease.2 Thus, calendar time could be a confounder of the observed association in this study. Failure to account for calendar time could result in an overestimate of the protective effect of colonoscopy. FATEN N. ABERRA, MD, MSCE MARK T. OSTERMAN, MD, MSCE JAMES D. LEWIS, MD, MSCE Division of Gastroenterology and Hepatology University of Pennsylvania Health System Perelman School of Medicine at the University of Pennsylvania Philadelphia, Pennsylvania
References 1.
Ananthakrishnan AN, et al. Clin Gastroenterol Hepatol 2015; 13:322–329.
2.
Herrinton LJ, et al. Gastroenterology 2012;143:382–389.
Conflicts of interest The authors disclose no conflicts. http://dx.doi.org/10.1016/j.cgh.2015.02.032
LETTER TO THE EDITOR Readers are encouraged to write letters to the editor concerning articles that have been published in Clinical Gastroenterology and Hepatology. Short, general comments are also considered, but use of the Letters to the Editor section for publication of original data in preliminary form is not encouraged. Letters should be typewritten and submitted electronically to http://www. editorialmanager.com/cgh.
Can Colonoscopy Reduce the Risk of Colon Cancer and Mortality in Patients With Inflammatory Bowel Disease? Dear Editor: We read with interest the study by Ananthakrishnan et al1 that showed that colonoscopy within 3 years is associated with a lower risk of colon cancer among patients with inflammatory bowel disease.1 This is an extremely important finding and the results of this study reinforce the need to follow current screening guidelines. Assuming that most of the patients in this study underwent standard white-light endoscopy, this study also raises the bar for future studies of contrast-enhanced endoscopy to show a greater reduction in colon cancer incidence than standard white-light colonoscopy, not just increased detection of dysplasia. However, before we fully accept the results of the current study, we ask that the authors clarify a few potential sources of bias that could have made colonoscopy look particularly effective. The authors reported that their exposure variable was completion of a colonoscopy performed in the 3 years before the index date, which was the date of the colon cancer diagnosis for cases and the end of the follow-up period for controls. They excluded colonoscopies performed in the 6 months immediately before the index date among the cases to avoid inclusion of the colonoscopy that led to the colon cancer diagnosis. This logic is sound but potentially creates a bias by allowing controls a 36-month period during which they could have undergone colonoscopy, whereas cases only had a 30-month period. To avoid this bias, the investigators also would need to exclude the same 6-month time period among the controls. The index date for cases (ie, the date of diagnosis of colorectal cancer) is likely the date of a colonoscopy because colonoscopy is the gold standard test for colon cancer diagnosis. In contrast, the index date of controls
was their last visit. Because colonoscopies are recommended in 1- to 3-year intervals, it is possible in the case group that the colonoscopy before diagnosis of colon cancer was immediately before the window for exposure, yet was in the window of exposure for controls because of the choice of index date. For example, if both case and control patients were undergoing a colonoscopy every 4 years, none of the cases vs 75% of controls would appear to have undergone a colonoscopy in the preceding 3 years despite comparable use of colonoscopy. To determine if this led to a biased result, extending the exposure window for both groups may help. Our last concern also relates to the choice of the end of the follow-up period as the index date among the controls. This likely resulted in the index date occurring, on average, in later years among controls than among cases. The use of surveillance colonoscopy has increased over time among patients with inflammatory bowel disease.2 Thus, calendar time could be a confounder of the observed association in this study. Failure to account for calendar time could result in an overestimate of the protective effect of colonoscopy. FATEN N. ABERRA, MD, MSCE MARK T. OSTERMAN, MD, MSCE JAMES D. LEWIS, MD, MSCE Division of Gastroenterology and Hepatology University of Pennsylvania Health System Perelman School of Medicine at the University of Pennsylvania Philadelphia, Pennsylvania
References 1.
Ananthakrishnan AN, et al. Clin Gastroenterol Hepatol 2015; 13:322–329.
2.
Herrinton LJ, et al. Gastroenterology 2012;143:382–389.
Conflicts of interest The authors disclose no conflicts. http://dx.doi.org/10.1016/j.cgh.2015.02.032