Gastric cancer, often called stomach cancer, arises most commonly from the glandular cells of the stomach lining and is usually classified as adenocarcinoma. Incidence varies widely across regions, with particularly high rates in East Asia, Eastern Europe and parts of South America. Overall numbers are declining in many countries, but it remains a major cause of cancer deaths worldwide.

A central risk factor is infection with the bacterium Helicobacter pylori, which can drive chronic inflammation, atrophic gastritis and eventually malignant transformation. Additional contributors include diets high in salted, smoked or pickled foods, low intake of fresh fruits and vegetables, smoking, heavy alcohol use, obesity and certain genetic predispositions. Autoimmune gastritis and previous gastric surgery also increase risk.

Research shows that gastric cancer is heterogeneous. Tumors differ in location, microscopic appearance and molecular profile. Some are linked to inherited mutations, such as in the CDH1 gene, which greatly increases the risk of diffuse type gastric cancer and sometimes leads to preventive gastrectomy in high risk families. Molecular classifications identify subgroups defined by features like Epstein–Barr virus positivity, microsatellite instability or specific gene alterations, which may guide targeted and immunotherapies.

Early stage disease is often silent or causes vague symptoms, so many patients present late. Endoscopy with biopsy is essential for diagnosis, and in some high risk countries screening programs have improved early detection. Treatment combines surgery, chemotherapy, radiotherapy and newer targeted agents or immune checkpoint inhibitors, depending on stage and tumor biology. Ongoing studies aim to refine prevention, improve early diagnosis and personalize therapy to improve survival and quality of life.