The purpose of this study is to establish a gastric cancer registry. A registry is a database of information. With the registry, we can learn more about the genetic causes of gastric cancer in order to develop better methods of early diagnosis, prevention, and treatment of gastric cancers. As part of this study, you will be asked to join a registry of families who are affected with various forms of gastric cancer. These registries are important because they may help physicians better manage gastric cancer now and in the future. Participating in the Early Onset and Familial Gastric Cancer Registry can also be educational for families, since it will provide important information to patients, families, and physicians. All of this will help to further our understanding of genetic causes of gastric cancer and eventually, help determine better ways to diagnose, treat, and survey patients with gastric cancer and people who may have a higher risk for gastric cancer.

Inclusion Criteria:

Patient/Relative Cohort:

Must meet one or more criteria below:

1. A person with a diagnosis of gastric or gastroesophageal junction (GEJ) adenocarcinoma confirmed at the treating institution.

2. A person without gastric or GEJ adenocarcinoma who has or had a first degree relative eligible for a High Risk Genetic sub-group (EOGC/FGC).

   1. Early Onset Gastric Cancer - diagnosis of gastric cancer before the age of 50 without a family history of the disease.
   2. Familial Gastric Cancer - having a family history of gastric cancer as defined as one first degree relative or 2 second degree relatives.

3. A person without gastric or GEJ adenocarcinoma who has a personal family history of a genetic mutation associated with the development of gastric or GEJ adenocarcinoma (i.e. family history of CDH1 mutation).

II. Must be willing to provide a blood sample for germline DNA. These individuals will sign the "Patient/Relative Consent". Following enrollment, we will assign individuals to the appropriate High Genetic Risk or Low Genetic Risk groups based on the age of diagnosis and their family history.

Subject Exclusion Criteria

Patients are ineligible for the study if they:

• Have any condition, which in the opinion of the primary MSK clinician or investigators precludes their ability to provide informed consent.
• Relatives of patients that are not eligible for the High Genetic Risk Cohorts who are less than 18 years of age are excluded.
• Relatives of patients eligible for the High Genetic Risk Cohorts who do not have a proband available to join the study are excluded. (Unless there is a known CDH1 mutation in the family).

Potential research subjects will be identified by a member of the patient's treatment team, the protocol investigator, or research team at MSK or collaborating centers. If the investigator is a member of the treatment team, s/he will screen their patient's medical records for suitable research study participation and discuss the study and their potential for enrolling in the research study. Potential subjects contacted by their treating physician will be referred to the investigator/research staff of the study.