Epidemiology, characteristics and survival of post-colonoscopy colorectal cancer in Hong Kong: a population-based study

Abstract

Introduction: Population-based studies on post-colonoscopy colorectal cancer (CRC) from Asia are sparse. We aimed to determine the characteristics and risk factors of post-colonoscopy CRC in Hong Kong. Methods: This is a retrospective cohort study recruiting patients aged ≥40 years undergoing colonoscopies between 2005 and 2013 based on a territory-wide electronic healthcare database in Hong Kong. Exclusion criteria included prior CRC, inflammatory bowel disease and prior colectomy. Post-colonoscopy CRC within 3 years (PCCRC-3y) was defined as CRC diagnosed between 6 and 36 months after index colonoscopy, while CRC diagnosed within 6 months of index colonoscopy was regarded as “detected CRC”. Sites of CRC were categorised as proximal (proximal to splenic flexure) and distal cancer. We used multivariable logistic regression to derive adjusted odds ratio (aOR) of PCCRC-3y, and Cox model for adjusted hazard ratio (aHR) of all-cause mortality after CRC diagnosis. Results: Of the 197 902 eligible patients, 10 005 (92.1%) were detected CRC and 854 (7.9%) PCCRC-3y (707 [82.8%] and 147 [17.2%] in the distal and proximal colon, respectively). The PCCRC-3y rate between 2005 and 2013 was 7.9%, with a significant increase in the PCCRC-3y rate from 4.1% to 9.7% (Poisson P<0.001) between 2005 and 2009, but a significant decrease from 9.7% to 7.7% (Poisson P=0.046) between 2009 and 2013. The median age at PCCRC-3y diagnosis was 75.9 (interquartile range [IQR], 65.5-83.8) years—a delay of 1.2 (IQR, 0.8-1.9) years from index colonoscopy—and 60.1% were men. Risk factors for PCCRC-3y included older age (aOR=1.07, 95% confidence interval [CI]=1.06-1.08), male sex (aOR=1.45, 95% CI=1.26-1.67), history of colonic polyps (aOR=1.31; 95% CI=1.13-1.51), polypectomy/biopsy at index colonoscopy (aOR=3.97; 95% CI=3.46-4.56), index colonoscopy by surgical specialty (aOR=1.53; 95% CI=1.31-1.78), and a higher annual colonoscopy volume of the centre. The median survival time was lower for patients with PCCRC-3y (1.9 years, 95% CI=1.7-2.6 years) when compared with those with detected CRC (5.2 years, 95% CI=4.8-5.6 years) [log-rank P<0.001]. Risk factors for all-cause mortality after CRC diagnosis included PCCRC-3y (aHR=1.31; 95% CI=1.19-1.43), proximal cancer location (aHR=1.42; 95% CI=1.31-1.54), and certain patient factors. Conclusions: The PCCRC-3y rate is 7.9% in Hong Kong, with a high proportion (>80%) of distal cancers and a higher overall mortality compared with detected CRC. Measures to improve colonoscopy quality are needed to reduce the incidence of PCCRC in Hong Kong.