The Workgroup Serrated Polyps and Polyposis (WASP) classification for optical diagnosis of colorectal diminutive polyps with iScan and the impact of the revised World Health Organization (WHO) criteria

Abstract

Background and aims: The Workgroup Serrated Polyps and Polyposis (WASP) developed criteria for optical diagnosis of colorectal polyps. The aims of this study were: (1) to improve optical diagnosis of diminutive colorectal polyps, especially SSLs, after training endoscopists in applying WASP criteria on videos of polyps obtained with iScan and (2) to evaluate if the WASP criteria are still useful when polyps are pathologically revised according to the World Health Organization (WHO) 2019 criteria.

Methods: Twenty-one endoscopists participated in a training session and predicted polyp histology on 30 videos of diminutive polyps, before and after training (T₀ and T₁ ). After three months, they scored another 30 videos (T₂ ). Primary outcome was overall diagnostic accuracy (DA) at T₀ , T₁ and T₂ . Polyps were histopathologically classified according to the WHO 2010 and 2019 criteria.

Results: Overall DA (both diminutive adenomas and SSLs) significantly improved from 0.58 (95% CI 0.55-0.62) at T₀ to 0.63 (95% CI 0.60-0.66, p = 0.004) at T₁ . For SSLs, DA did not change with 0.51 (95% CI 0.46-0.56) at T₀ and 0.55 (95% CI 0.49-0.60, p = 0.119) at T₁ . After three months, overall DA was 0.58 (95% CI 0.54-0.62, p = 0.787, relative to T₀ ) while DA for SSLs was 0.48 (95% CI 0.42-0.55, p = 0.520) at T₂ . After pathological revision according to the WHO 2019 criteria, DA of all polyps significantly changed at all time points.

Conclusion: A training session in applying WASP criteria on endoscopic videos made with iScan did not improve endoscopists' long-term ability to optically diagnose diminutive polyps. The change of DA following polyp revision according to the revised WHO 2019 criteria suggests that the WASP classification may need revision.

Keywords: WASP classification; adenoma; colorectal polyp; diagnostic accuracy; endoscopist training; endoscopy; hyperplastic polyp; iScan; optical diagnosis; sessile serrated lesion.