International guidelines recommend deciding the treatment of colorectal lesions based on the estimated histology by endoscopic optical diagnosis. However, the theoretical and practical knowledge on optical diagnosis is not widely expanded

The mail goal of this randomised controlled trial is to compare the pooled sensitivity of optical diagnosis for predicting deep submucosal invasion in large non-pedunculated polyps > 20 mm assessed in routine colonoscopies of gastroenterologists attending a e-learning module (intervention group) vs gastroenterologists who do not (control group)

The main questions the study aims to answer are:

• Is the pooled sensitivity of optical diagnosis for predicting deep submucosal invasion in large non-pedunculated polyps assessed in routine colonoscopies increased in those gastroenterologists participating in the e-learning module?
• Is the pooled diagnostic accuracy of optical diagnosis for predicting deep sm invasion in large non-pedunculated polyps ≥ 20 mm assessed in routine colonoscopies increased in those gastroenterologists participating in the e-learning module?
• In lesions with submucosal invasion, is the en bloc and complete resection rate (R0) increased in those gastroenterologists participating in the e-learning module?
• In lesions referred to surgery, is the pooled benign polyps rate decreased in those gastroenterologists participating in the e-learning module?
• In lesions treated with advanced en bloc procedures (ESD, TAMIS, fullthickness resection), is the pooled rate of histology with high-grade dysplasia, intramucosal cancer or submucosal invasion increased in those gastroenterologists participating in the e-learning module?
• In lesions treated with piecemeal endoscopic resection, is the pooled rate of histology with high-grade dysplasia, intramucosal cancer or submucosal invasion decreased in those gastroenterologists participating in the e-learning module?
• Is the diagnostic accuracy for predicting deep submucosal invasion in a test with pictures increased after participating in the e-learning module?

The participants (or subjects of study) are gastroenterologists. They will be randomised to do the e-learning course (intervention group) or not (control group).

Researchers will compare clinical outcomes of gastroenterologists participating in the e-learning module vs gastroenterologists not participating in the e-learning module to see if:

• the pooled sensitivity of optical diagnosis for predicting deep submucosal invasion in large non-pedunculated polyps > 20 mm assessed in routine colonoscopies is increased.
• the pooled diagnostic accuracy of optical diagnosis for predicting deep sm invasion in large non-pedunculated polyps > 20 mm is increased.
• the en bloc and complete resection rate (R0) is increased in lesions with submucosal invasion.
• the pooled benign polyps rate decreased in lesions referred to surgery.
• the pooled rate of histology with high-grade dysplasia, intramucosal cancer or submucosal invasion increased in lesions treated with advanced en bloc procedures (ESD, TAMIS, fullthickness resection).
• the pooled rate of histology with high-grade dysplasia, intramucosal cancer or submucosal invasion decreased in lesions treated with piecemeal endoscopic resection.
• the diagnostic accuracy for predicting deep submucosal invasion in a test with pictures after participating is increased.

Non-pharmacological multi-centre randomised controlled trial. Gastroenterologists who have performed > 300 colonoscopies without supervision and who have finished/will finish the residency in Gastroenterology between 2014 and 2023 will be invited to participate. Gastroenterologists participating in the study will register the optical diagnosis, endoscopic lesions' characteristics, histology and clinical outcomes of consecutive non-pedunculated lesions ≥ 20 mm found in routine colonoscopies during a whole year. Participants allocated in the intervention group will receive a learning module after six months. Those assigned in the control group will not receive any learning module (they will be offered to do it at the end of the study). Pooled sensitivity and diagnostic accuracy of optical diagnosis for predicting deep submucosal invasion, and clinical outcomes in routine colonoscopies will be compared in both groups. Diagnostic accuracy for predicting deep submucosal invasion in a test with pictures before and after participating will also be compared.

Inclusion Criteria:

• Gastroenterologists who have performed > 300 colonoscopies without supervision and are in the last training year or had finished the Gastroenterology residency after 2014.

Exclusion Criteria:

• Endoscopists who have learned the invasive pattern in a centre where endoscopists have published a high diagnostic accuracy for predicting deep submucosal invasion (Japanese centres).