This prospective multicenter study investigates the added benefit of incisura biopsy to correct identification of patients with high-risk chronic gastritis (OLGA stages III-IV). It compares a biopsy protocol with and without a single incisura biopsy in a non-inferiority design. Anonymized photo and videodocumentation according to institution practices will constitute a databank for lesion recognition, quality improvement, and potential AI development.

The investigators will perform a prospective, multicenter, randomized controlled trial of 2 different gastric biopsy protocols. The hypothesis is that a gastric mapping protocol not including the incisura biopsy ("I-": 2 biopsies from the antrum, 2 from the corpus) is non-inferior to the conventional 5-biopsy approach ("I+": 2 biopsies from the antrum, 2 from the corpus, 1 from the incisura). The primary endpoint of this study is to assess the sensitivity of the "I-" protocol in diagnosing high-risk precancerous chronic gastritis (OLGA/OLGIM stages III or IV) compared to the assumed gold standard of histology based on the "I+" protocol.

In designing the study, the investigators opted for a non-inferiority paired design with high-risk chronic gastritis as a primary binary outcome and a non-inferiority margin (Δ) of 5 % (two-sided 95% CI). The non-inferiority margin was established according to clinical judgement, taking into consideration the significance of a missed diagnosis of high-risk preneoplastic condition and previous estimates of the added value offered by the added incisura biopsy. With a power of 80% and a 2-sided α-level set at 0.05, it is estimated that 370 subjects are needed to show non-inferiority. Finally, 400 subjects will be enrolled to compensate for eventual exclusions or protocol deviations.

Cohen's kappa will be used to rate intra and inter-observer concordance for pathologists.

An intermediary analysis for futility is scheduled after 100 patients (25%) are enrolled.

Inclusion Criteria:

• indication to perform upper GI endoscopy for diagnosis or surveillance

Exclusion Criteria:

• lack of informed consent, previously diagnosed advanced gastric cancer, incomplete endoscopy, surgically altered stomach

All patients over 18 years undergoing upper GI endoscopy are considered eligible for this study, regardless of gender, age or indication.

Anonymized data and images from endoscopy and pathology are shared between participating centers according to the protocol.

The data will be available during the study period, after enrollment of all participants. Possible usage of the anonymized database will be discussed by study investigators.

reasonable request