Gastric cancer

Gastric cancer originates from the mucosal epithelial cells on the outermost layer of the gastric wall. It can occur in various parts of the stomach (most commonly in the gastric antrum and pyloric region, followed by the gastric fundus and cardia region, and slightly less in the gastric body), and can invade the gastric wall to different depths and extents. Lesions confined to the mucosa or submucosa are called early gastric cancer; those invading beyond the muscularis propria or with metastasis to areas outside the stomach are called advanced gastric cancer. On gross examination or gastroscopy, gastric cancer has various morphological forms, such as superficial type, mass type, ulcerative type, infiltrative type, and ulcerating carcinoma (malignant transformation of a chronic gastric ulcer). Under microscopic magnification, cancer cells have various types (histological classification), such as adenocarcinoma (accounting for about 90%, including papillary adenocarcinoma, tubular adenocarcinoma, mucinous adenocarcinoma, and signet ring cell carcinoma), adenosquamous carcinoma, squamous cell carcinoma, undifferentiated carcinoma, and carcinoid tumor. There are also many differences in the molecular structure within the finer cancer cells. Therefore, although all are called gastric cancer, even if the types seen under gross examination and microscopy are the same, there are still great differences in their biological behavior. Currently, it is not known exactly how many individually distinct types of gastric cancer exist.