Stomach cancer

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.

• Stage 0 cancer is limited to the inner lining of the stomach. When found at this early stage, possibly in routine screenings, the tumor is treatable by endoscopic mucosal resection, or by gastrectomy and lymphadenectomy without a need for chemotherapy or radiation.

• Stage I tumors penetrate to the second or third layers of the stomach (IA) or to the second layer and nearby lymph nodes (IB). Stage IA is treated by surgery, including removal of the omentum. Stage IB may in addition to surgery, be treated with chemotherapy (5-fluorouracil) and radiation therapy.

• Stage II tumors penetrate to the second layer of the stomach and involve more distant lymph nodes, to the third layer and only nearby lymph nodes, or to all four layers but not to lymph nodes. Treatment is the same as for Stage I tumors, sometimes with the addition of neoadjuvant chemotherapy.

• Stage III is characterized by penetration to the third layer and metastases in more distant lymph nodes, or penetration to the fourth layer and tumor growth in either surrounding tissues or regional/distant lymph nodes. The disease is treated as in Stage II and in some cases a cure is still possible. In Stage IV the cancer has spread to nearby tissues and more distant lymph nodes, or has metastasized to distant organs. A cure is very rarely possible at this stage. Treatment to prolong life or reduce symptoms may be implemented, including laser treatment, chemotherapy, surgery, and/or stents to keep the digestive tract open.

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.