Analysis of Post-Colonoscopy Colorectal Cancer and Its Subtypes in a Screening Programme

SIMPLE SUMMARY: This study responds to the algorithm proposed by the World Endoscopy Organization (WEO) and adapts well to the surveillance of the adverse effects of the population-based colorectal cancer (CRC) screening programmes (interval cancers). In our case, the application of the aforementioned algorithm to the Basque Country Programme, which began in 2009 and reached coverage of around 100% in 2014, has been an opportunity to evaluate in a standardised way the cancers detected after a colonoscopy carried out following a positive Faecal Immunochemical Test (FIT). All the characteristics found in these cancers and their relationship with the index colonoscopy have been described. The differences in both the stage and the quality of the colonoscopies and the lesions detected must be taken into consideration, in order to evaluate the surveillance and to reduce one of the adverse effects on a CRC screening programme, as far as possible. ABSTRACT: Using the algorithm of the World Endoscopy Organisation (WEO), we have studied retrospectively all colorectal cancers, both detected and non-detected by the Basque Country screening programme from 2009 to 2017. In the screening programme 61,335 colonoscopies were performed following a positive Faecal Immunochemical test (FIT) (≥20 µg Hb/g faeces) and the 128 cases of post-colonoscopy colorectal cancer (PCCRC) detected were analysed. Among them, 50 interval type PCCRCs were diagnosed (before the recommended surveillance), 0.8 cases per 1000 colonoscopies performed, and 78 non-interval type PCCRCs (in the surveillance carried out at the recommended time or delayed), 1.3 per 1000 colonoscopies. Among the non-interval type PCCRCs, 61 cases were detected in the surveillance carried out at the recommended time (type A) and 17 when the surveillance was delayed (type B), 1 case per 1000 colonoscopies performed and 0.28 cases per 1000 colonoscopies performed, respectively. Interval type PCCRC is less frequent than non-interval type PCCRC. In interval type PCCRCs, CRCs detected in advanced stages (stages III–IV) were significantly more frequent than those detected in early stages, compared to those of non-interval type PCCRCs (OR = 3.057; 95% CI, 1.410–6.625; p < 0.005). Non-interval type B PCCRCs are less frequent than non-interval type A PCCRCs, but the frequency of advanced stages is higher in interval type B PCCRCs.