PTH-021 Cancer and adenoma detection rate in 2-week wait colonoscopy and CT colonography- tertiary centre experience

Abstract

Introduction Computed Tomography Colonoscopy (CTC) is increasingly being used as an alternative to optical colonoscopy (OC). The SIGGAR trial and COCOS study have shown CTC to be an accurate and safe alternative to OC for diagnosis of colorectal cancer (CRC) and large polyps. Our aim was to compare various performance indicators between CTC and OC in the lower GI straight to test (STT) 2 week wait (2 WW) pathway. Methods The investigation of choice for the lower GI 2 WW STT cohort between Nov 2014 and Oct 2015 was OC with CTC being the first-line test between Jan 2016 and Dec 2016. We retrospectively analysed 12 months’ data for both cohorts. Outcomes included completion rate, polyp detection rate (PDR), adenoma detection rate (ADR) and CRC detection rates. Results 1135 patients attended for OC versus 1829 for CTC. Significantly more OC were cancelled on the day compared to CTC (6.5% v 2% p=0.0001). OC had a completion rate measured by caecal intubation of 86% versus 100% of CTC (p=0.0001). The diagnostic study rate measured by adequate bowel preparation/faecal tagging and distension was 89.3% at OC (adequate preparation) versus 98.4% for CTC (p=0.0001). CRC detection rate was 4.5% (95% CI 3.43% to 5.95%) in the OC group versus 4.9% (95% CI 3.97% to 5.95%) in the CTC group (p=>0.005). The PDR was significantly higher in the OC group compared to the CTC group (25.1% (95% CI 22.95% to 27.32%) v 13.5% (95% CI 11.95% to 15.11%) p=0.0001). However, 61.7% of the polyps detected at OC were ≤5 mm which are not routinely reported on CTC. PDR for polyps>5 mm at OC was 9.6% (95% CI 7.98% to 11.54%) versus 13.5% at CTC (p=0.0024). The ADR at OC was significantly higher than in the CTC (16.5% (95% CI 14.38% to 18.85%) versus 9.8% (95% CI 8.53% to 11.29%) p=0.0001). The non-CRC detection rate in the CTC group was 4.3%. Conclusions CTC and OC have comparable CRC detection rates for patients referred via the 2 WW STT lower GI pathway. However, the PDR and ADR are higher with OC, this data is skewed by the number of diminutive polyps identified at OC that are not routinely reported at CTC. Also, a number of cases with 5–10 mm polyps at CTC did not progress to OC. Long term follow up data is required to compare interval cancer detection rates in these cohorts to assess the impact of not reporting/identifying sub 5 mm polyps. From a service delivery perspective, the on the day cancellation rate, completion rate and diagnostic study rate for CTC were significantly better than OC in the STT patient. An additional benefit of CTC is the diagnosis of non-colonic cancers, the rate of which was comparable to the CRC rate.