The goal of this observational study is to evaluate the risk factors associated with incident HGD/GA in patients with CAG with or without IM who are enrolled in endoscopic surveillance, as well as to compare GA incidence according to the OLGA and OLGIM scales in patients 18 years or older.

. The main questions it aims to answer are:

• What risk factors are associated with incident HGD/GA in patients with CAG with or without IM?
• What is the comparative HGD/GA incidence according to the OLGA and OLGIM scales?

The Endoscopic Cohort and Histological OLGA staging (ECHOS) study is a retrospective longitudinal cohort developed in the Pontificia Universidad Católica de Chile health care system, an open health care system with 3 endoscopic units in Santiago, Chile. Patients 18 years or older were eligible for the study if they had at least one non-urgent outpatient EGD with gastric biopsies collected following the USSBP between June 2015 and June 2021. The baseline EGD was defined as the earliest examination conducted between this time frame that met inclusion criteria. Participants were included in the cohort if they underwent a subsequent "surveillance" EGD. In order for the subsequent EGD to qualify as surveillance, it needed to occur at least 6 months after the baseline EGD and include gastric biopsies collected according to the USSBP; one exception to the USSBP requirement was if HGD or GA was detected on the surveillance (i.e. non-baseline) EGD. Patients with prior history of HGD or any type of gastric malignancy, gastrectomy or non-gastric active malignancy were excluded. Also, patients with HGD or GA on the baseline EGD were excluded. Patients with indefinite (IND) or low-grade dysplasia (LGD) on the baseline EGD were considered for the cohort.

Inclusion Criteria:

• At least one non-urgent outpatient esophagogastroduodenoscopy (EGD) with gastric biopsies collected following the Updated Sydney System Biopsy Protocol (USSBP) between June 2015 and June 2021.
• Underwent a subsequent "surveillance" EGD. For the subsequent EGD to qualify as surveillance, it needed to occur at least six months after the baseline EGD and include gastric biopsies collected according to the USSBP; one exception to the USSBP requirement was if HGD or GA was detected on the surveillance.

Exclusion Criteria:

• Prior history of HGD or any type of gastric malignancy, gastrectomy, or non-gastric active malignancy.
• HGD or GA on the baseline EGD was excluded.

Patients atteding an EGD at Pontificia Universidad Católica de Chile health care system, an open health care system with three endoscopic units in Santiago, Chile.