Stomach cancer, also termed gastric cancer or gastric carcinoma, originates from the mucosa of the stomach. Helicobacter pylori infection is a main risk factor for development of stomach cancer. A history of adenomatous gastric polyps larger than two centimeters, chronic atrophic gastritis, or pernicious anemia are other risk factors, as are smoking and consumption of salted, cured or smoked foods. A genetic component is present in approximately 10 % of cases. Stomach cancer occurs most often in men over the age of 40 and is common in Japan, Chile, and Iceland. The diagnosis of stomach cancer is often based on biopsy material obtained through gastroscopy.
Adenocarcinoma is the most common type of stomach cancer. Depending on glandular architecture, cellular pleomorphism and secretion of mucins, the cancer is defined as well, moderately, or poorly differentiated. Histologically, there are two main types of adenocarcinoma: intestinal and diffuse. The intestinal subtype is composed of irregular glands that have a back-to-back appearance with loss of surrounding stroma. Cells that show nuclear atypia line the glands. The diffuse subtype of stomach cancer is composed of loosely cohesive cells that secrete mucus into the interstitium. Signet-ring cells, in which the mucus remains within the cytoplasm and pushes the nucleus to the periphery, are often a component of this tumor type.
Cancer stage is assessed using the TNM system, which describes the extent of the primary tumor (T), the absence or presence of spread to nearby lymph nodes (N) and the absence or presence of distant spread, or metastasis (M). Once the T, N and M are determined, a stage of 0, I, II, III or IV is assigned.
Approximately 50% of adenocarcinomas in the stomach express cytokeratin 7 (KRT7) and 75% are positive for cytokeratin 20 (KRT20). Stomach cancer is SATB2 negative, a finding that aids in distinguishing them from metastatic colorectal cancer.