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.
