This study is a multi-center, prospective cohort study which are planned to enroll the 2,500 patients who diagnosed the primary gastric cancer and 5,000 healthy normal cohort participants for 5 years. All participants who enrolled in this registry, the participants were questioned by the gastric cancer survey and the serum and tissue of these participants were analyzed.

The main aim of this study is

1. To evaluate the optimal interval of endoscopic screening for early detection of gastric cancer and risk factors in Korean.
2. To evaluate the diagnostic validity of serum biomarker (combining pepsinogen, H pylori IgG Antibody, and TFF3) as a screening test for detection of GC in Korean.

Gastric cancer (GC) is the fourth most common type of cancer (934 000 new cases, 8.6% of all new cancer cases in 2002), and the second most common cause of cancer death (700 000 deaths annually) in the world. Several Asian countries, including China, Japan, and Korea, have the highest incidences of GC in the world. Because the prognosis of early GC is highly favorable, high- prevalence countries, such as Japan and Korea, have sought to reduce the disease burden by providing GC screening to aver- age-risk populations. In Korea, national GC screening was instituted in 1999 as part of the National Cancer Screening Program (NCSP). The NCSP recommends biennial GC screening for males and females older than 40 years of age, using direct or indirect upper gastrointestinal series (UGIS) or endoscopy. Upper gastrointestinal endoscopies are generally accepted as the gold standard for the diagnosis and clinicopathological evaluation of GC. Endoscopic examination has been predominantly used to screen symptomatic individuals, and to distinguish patients with GC from those with comparatively benign diseases, such as peptic ulcers. However, there was no consensus for optimal timing of screening endoscopy to detect of early GC.

Thus, investigators are planned to evaluate the optimal endoscopic interval to find early gastric cancer by use of survey between newly diagnosed GC cohort group and healthy control cohort group. In addition, investigators are going to analyze the risk factors of GC in Korean (epidemiologic, diet, and clinical factors). In this study, the investigators are going to enroll the participants who were diagnosed GC and normal control group people, from October 2016 to October 2021 in multi-center, prospectively. The baseline characteristics of the participants, H. pylori status, stage of gastric cancer at diagnosis, treatment modalities, treatment response and mortality were analyzed.

Although diagnosis of gastric cancer has been characterized by endoscopy, there has been a strong demand for serologic marker because accessibility, invasiveness, discomfort of endoscopy. In recent years, there have been advancements in the molecular biomarkers utilized in the cancer detection and in the development of therapeutic agents based on the target genes for a few types of solid tumours excluding GC. With the advancement of molecular biological techniques in the last decades, researchers have gained important insights into the oncogenesis mechanisms of GC. Besides the well-known pathogenic factor, Helicobacter pylori, various experimental approaches have identified oncogenes and tumour suppressor genes, including cell cycle regulation genes in the growth and signal transduction pathways. Recently, several studies were reported about the efficacy of the serum biomarker (serum PG, H. pylori Ig G Antibody and TFF3, etc) for diagnosis of GC. In this present study, investigators are going to the efficacy of serum biomarker by the use of serum of GC patients and health control group.

Inclusion Criteria:

• The patients who were diagnosed of primary gastric adenocarcinoma and drew up agreement for understanding and enrollment of this study.

Exclusion Criteria:

• Being treated (surgery, endoscopic resection and chemoradiation) after the diagnosis of gastric cancer; metastatic gastric cancer; refusal to participation of this study

This cohort study is designed to enroll the patients who are diagnosed gastric cancer and healthy control participants by multicenter-prospective registry. From now on, we are willing to enroll about 2,500 gastric cancer patients and about 5,000 control group for 5 years.