Confocal Endoscopic Microscopy for Detection of Early Stage Gastric Cancer in Subjects With Hereditary Diffuse Gastric Cancer Syndrome

Background: People with hereditary gastric cancer syndrome are at increased risk of getting cancer in their stomach. These people should have regular endoscopies and biopsies to check for cancer if they are choosing to keep their stomach. Researchers want to see if they can improve the detection of cancer by endoscopy. Improved endoscopies could better detect early signs of cancer in people with this syndrome. Objective: To see if a small microscope attached to an endoscope to inspect the stomach lining is better than regular endoscopy to find the first signs of cancer in the stomach. Eligibility: People ages 18 and older who have a personal or family history of a hereditary gastric cancer syndrome or have a mutation that is known to lead to gastric cancer Design: Participants will be screened over the phone or in person with: * Personal and family medical history * Review of their medical records Participants will have a physical exam. Then they will be put under general anesthesia. They will have an endoscopy. A lighted tube will be inserted into the mouth and go down to the stomach. First, the standard device will be used. Then participants will be injected with fluorescein. This is a contrast agent. Then the microscope will be added to the tube and the endoscopic evaluation of the stomach will be repeated. During the procedure, biopsies will be taken from different areas of the stomach. Participants will be observed for a few hours after the procedure. About 14 days after the endoscopy, participants will be asked to return to the clinic for a follow-up visit. This visit can also be conducted over the phone.