Increased colorectal cancer risk during follow-up in patients with hyperplastic polyposis syndrome: a multicentre cohort study.Boparai KS, Mathus-Vliegen EM, Koornstra JJ, Nagengast FM, van Leerdam M, van Noesel CJ, Houben M, Cats A, van Hest LP, Fockens P, Dekker E. Gut. 2009 Aug 25. [Epub ahead of print] BACKGROUND AND AIMS: Patients with hyperplastic polyposis syndrome (HPS) receive endoscopic surveillance to prevent malignant progression of polyps. However, the optimal treatment and surveillance protocol for these patients is unknown. The aim of this study was to describe the clinical and pathological features of a large HPS cohort during multiple years of endoscopic surveillance. METHODS: Databases were searched for HPS patients who were retrospectively analysed. Endoscopy reports and histopathology reports were collected to evaluate frequency of endoscopic surveillance and to obtain information regarding polyp and CRC presence. RESULTS: In 77 HPS patients, 1984 polyps were identified during a mean follow-up period of 5.6 years (range:0.5-26.6). In 27(35%) patients CRC was detected of which 22(28.5%) at initial endoscopy. CRC was detected during surveillance in five patients (cumulative incidence: 6.5%) after a median follow-up time of 1.3 years and a median interval of 11 months. Of these interval CRCs, 4/5 were detected in diminutive serrated polyps (range: 4-16mm). The cumulative risk of CRC under surveillance was 7% at five years. At multivariate logistic regression, an increasing number of hyperplastic polyps (odds ratio:1.05, p=0.013) and serrated adenomas (odds ratio:1.09, p=0.048) was significantly associated with CRC presence. CONCLUSIONS: HPS patients undergoing endoscopic surveillance have an increased CRC risk. The number of serrated polyps is positively correlated with the presence of CRC in HPS, thus supporting a ‘serrated pathway’ to CRC. To prevent malignant progression, adequate detection and removal of all polyps seems advisable. If this is not feasible, surgical resection should be considered.