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Original article
Development and validation of the WASP classification system for optical diagnosis of adenomas, hyperplastic polyps and sessile serrated adenomas/polyps
  1. Joep E G IJspeert1,
  2. Barbara A J Bastiaansen1,
  3. Monique E van Leerdam2,
  4. Gerrit A Meijer3,
  5. Susanne van Eeden4,
  6. Silvia Sanduleanu5,
  7. Erik J Schoon6,
  8. Tanya M Bisseling7,
  9. Manon CW Spaander8,
  10. Niels van Lelyveld9,
  11. Marloes Bargeman10,
  12. Junfeng Wang11,
  13. Evelien Dekker1,
  14. Dutch Workgroup serrAted polypS & Polyposis (WASP)
    1. 1Department of Gastroenterology and Hepatology, Academic Medical Center, Amsterdam, The Netherlands
    2. 2Department of Gastroenterology and Hepatology, Netherlands Cancer Institute, Amsterdam, The Netherlands
    3. 3Department of Pathology, Vrije Universiteit Medical Center, Amsterdam, The Netherlands
    4. 4Department of Pathology, Academic Medical Center, Amsterdam, The Netherlands
    5. 5Division of Gastroenterology and Hepatology, Maastricht University Medical Center, Maastricht, The Netherlands
    6. 6Department of Gastroenterology and Hepatology, Catharina Hospital, Eindhoven, The Netherlands
    7. 7Department of Gastroenterology and Hepatology, Radboud University Medical Centre, Nijmegen, The Netherlands
    8. 8Department of Gastroenterology and Hepatology, Erasmus University Medical Centre, Rotterdam, The Netherlands
    9. 9Department of Gastroenterology and Hepatology, St. Antonius Hospital, Nieuwegein, The Netherlands
    10. 10Department of Gastroenterology and Hepatology, Medical Spectrum Twente, Enschede, The Netherlands
    11. 11Department of Clinical Epidemiology, Biostatistics & Bioinformatics, Academic Medical Centre, University of Amsterdam, Amsterdam, The Netherlands
    1. Correspondence to Dr Evelien Dekker, Department of Gastroenterology and Hepatology, Academic Medical Centre, Meibergdreef 9, Amsterdam 1105 AZ, The Netherlands; e.dekker{at}


    Objective Accurate endoscopic differentiation would enable to resect and discard small and diminutive colonic lesions, thereby increasing cost-efficiency. Current classification systems based on narrow band imaging (NBI), however, do not include neoplastic sessile serrated adenomas/polyps (SSA/Ps). We aimed to develop and validate a new classification system for endoscopic differentiation of adenomas, hyperplastic polyps and SSA/Ps <10 mm.

    Design We developed the Workgroup serrAted polypS and Polyposis (WASP) classification, combining the NBI International Colorectal Endoscopic classification and criteria for differentiation of SSA/Ps in a stepwise approach. Ten consultant gastroenterologists predicted polyp histology, including levels of confidence, based on the endoscopic aspect of 45 polyps, before and after participation in training in the WASP classification. After 6 months, the same endoscopists predicted polyp histology of a new set of 50 polyps, with a ratio of lesions comparable to daily practice.

    Results The accuracy of optical diagnosis was 0.63 (95% CI 0.54 to 0.71) at baseline, which improved to 0.79 (95% CI 0.72 to 0.86, p<0.001) after training. For polyps diagnosed with high confidence the accuracy was 0.73 (95% CI 0.64 to 0.82), which improved to 0.87 (95% CI 0.80 to 0.95, p<0.01). The accuracy of optical diagnosis after 6 months was 0.76 (95% CI 0.72 to 0.80), increasing to 0.84 (95% CI 0.81 to 0.88) considering high confidence diagnosis. The combined negative predictive value with high confidence of diminutive neoplastic lesions (adenomas and SSA/Ps together) was 0.91 (95% CI 0.83 to 0.96).

    Conclusions We developed and validated the first integrative classification method for endoscopic differentiation of small and diminutive adenomas, hyperplastic polyps and SSA/Ps. In a still image evaluation setting, introduction of the WASP classification significantly improved the accuracy of optical diagnosis overall as well as SSA/P in particular, which proved to be sustainable after 6 months.


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