i. To determine whether Confocal Laser Endomicroscopy (CLE) with optical biopsy and targeted mucosal biopsy improves the diagnostic yield of gastric IM/IN/CA in high risk populations compared to WLE with standard biopsy protocol.

ii. To determine whether CLE with optical biopsy and targeted biopsy, as compared to WLE with standard biopsy, can reduce the number of biopsies needed per patient for detection of gastric IM/IN/carcinoma without the loss of corresponding diagnostic yield.

iii. To compare the sensitivity and specificity of CLE with WLE for the detection of gastric IM/IN/CA.

Gastric cancer remains the world's second leading cause of cancer-related deaths. The prognosis for patients with this cancer clearly depends on stage at diagnosis. At least for the intestinal subtype of gastric adenocarcinoma, a cascade of histopathologic lesions has been defined: chronic gastritis, atrophic chronic gastritis, intestinal metaplasia (IM), and intraepithelial neoplasia (IN). The identification of these lesions and follow-up of patients in whom they are found could lead to diagnosis of gastric cancer at an early stage, thus improving patients' survival. The diagnosis of these lesions, which often appear in flat mucosa, is currently based on histopathologic examination of endoscopic biopsy specimens. However, conventional white-light endoscopy (WLE) for this purpose has high interobserver variability and a poor correlation with histopathologic finding.

Confocal laser endomicroscopy (CLE), producing both conventional WLE and confocal microscopic images, can provide a direct histological observation of the in vivo tissue without the need for biopsy. Recently, CLE has shown its value for diagnosing gastric IM, intraepithelial neoplasia and carcinoma. However, none of those CLE criteria for gastric IM, IN or carcinoma (CA) has been validated in various endoscopic centers, hence reducing the reliability and clinical application of them.

Inclusion Criteria:

• Male or Female aged 18-80
• Patients with H. pylori infection, or histologically verified gastric intestinal metaplasia, low-grade intraepithelial neoplasia, and atrophic gastritis

Exclusion Criteria:

• Patients with gastrectomy, acute GI bleeding, and advanced gastric cancer
• Patients under conditions unsuitable for performing CLE including coagulopathy, impaired renal function, pregnancy or breastfeeding, and known allergy to fluorescein sodium
• Inability to provide informed consent and other situations that could interfere with the examination protocol