Stomach cancer also termed gastric cancer or gastric carcinoma, originates from the mucosa of the stomach. Stomach cancer occurs most often in men over the age of 40 and is common in Central and South America, Eastern Europe, and East Asia (China and Japan). Helicobacter pylori infection is the main risk factor for the development of stomach cancer. 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 food. A genetic component is present in approximately 10 % of cases including hereditary diffuse gastric cancers caused by mutations in cadherin 1 (CDH1) gene.
Symptoms of stomach cancer are chronic abdominal pain, chronic anemia, and weight loss. The diagnosis of stomach cancer is often based on biopsy material obtained through gastroscopy.
There are two main systems used to classify stomach cancer into histological subtypes: Lauren and World Health Organization (WHO) classification. Lauren classification is restricted to adenocarcinoma subtypes, while WHO classification is very detailed and encompasses other rare types such as neuroendocrine neoplasms.
Adenocarcinoma is the most common type of stomach cancer. By Lauren classification, there are two main types of adenocarcinoma: intestinal and diffuse. The intestinal subtype is composed of irregular glands with a back-to-back appearance and 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. According to WHO classification, there are several histological subtypes of adenocarcinoma based on different growth patterns. Depending on glandular architecture, cellular pleomorphism, and secretion of mucins, adenocarcinoma is graded as well, moderately, or poorly differentiated.
Diagnosis of stomach cancer is usually made based on morphological features. Immunohistochemistry is used in cases of poorly differentiated tumors to discriminate between primary gastric carcinoma and metastatic tumors, including lymphomas, or to exclude neuroendocrine differentiation. 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. Immunohistochemistry with antibody against HER-2 (ERBB2) is used for the selection of patients for treatment with monoclonal antibodies against HER-2.
Prognosis in patients with gastric tumors depends on the histological type and stage of the disease. Adenocarcinomas of intestinal type have a better prognosis than diffuse types. Treatment depends on the tumor stage, location of the tumor in the stomach, HER-2 (ERBB2) status, and patient’s overall health.