Background. This work examines the occurrence of interval colorectal cancers (CRCs) in the Ontario ColonCancerCheck (CCC)\nprogram. We define interval CRC as CRC diagnosed within 2 years following normal guaiac fecal occult blood testing (gFOBT).\nMethods. Persons aged 50ââ?¬â??74 who completed a baseline CCC gFOBT kit in 2008 and 2009, without a prior history of CRC, or recent\ncolonoscopy, flexible sigmoidoscopy, or gFOBT, were identified. Rates of CRC following positive and normal results at baseline and\nsubsequent gFOBT screens were computed and overall survival was compared between those following positive and normal results.\nResults. Interval CRC was diagnosed within 24 months following the baseline screen among 0.16% of normals and following the\nsubsequent screen among 0.18% of normals. Interval cancers comprised 38.70% of CRC following the baseline screen and 50.86%\nfollowing the subsequent screen. Adjusting for age and sex, the hazard ratio (HR) for death following interval cancer compared\nto CRC following positive result was 1.65 (1.32, 2.05) following the first screen and 1.71 (1.00, 2.91) following the second screen.\nConclusion. Interval CRCs following gFOBT screening comprise a significant proportion of CRC diagnosed within 2 years after\ngFOBT testing and are associated with a higher risk of death.
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