Stomach cancer occurs when the mucous cells lining the stomach develop abnormalities and become cancerous. The most common type of stomach cancer is adenocarcinoma, which accounts for 90% of all stomach cancer cases. Other rare types of stomach cancer occur in different areas of the stomach and include gastric lymphomas, gastrointestinal stromal tumors (GISTs), and carcinoid tumors.
Gastric lymphomas are cancers of the stomach’s immune system tissue.
Gastrointestinal stromal tumors (GISTs) can be either non-cancerous (benign) or cancerous and form in a special type of stomach wall cells called the interstitial cells of Cajal, which is a type of muscle tissue.
Carcinoid tumors originate in the endocrine and nervous systems and are slow-growing.
Stomach cancer is rare before age 50, mostly occurs in individuals over the age of 60, and is common in Japan.
While high rates of stomach cancer still occur globally, the overall rates have significantly decreased over the past twenty years.
Stomach cancer is categorized based on the following stages:
Stage 0 – Carcinoma in Situ is where cell abnormalities occur in the lining of the stomach (mucosa) which may become cancerous and spread (metastasis).
Stage 1 (IA and IB) – Cancer has developed in the lining of the stomach (mucosa) and may have spread to the next layer of the stomach (submucosa); Cancer has developed in the lining of the stomach (mucosa) and may have spread to the next layer of the stomach (submucosa) and 1 or 2 near lymph nodes or the stomach muscle layer.
Stage II (IIA and IIB) – Cancer may have spread to next lining of stomach (submucosa) and 3- to-6 near lymph nodes; or spread to stomach muscle layer and 1 or 2 near lymph nodes; or has spread to layer of stomach connective tissue. Cancer may have spread to outer lining of stomach (submucosa) and 7-to-15 near lymph nodes; or has spread to stomach muscle layer and 3-to-6 lymph nodes; or has spread to layer of stomach connective tissue and 1 or 2 near lymph nodes; or has spread to the outer wall of the stomach (serosa).
Stage III (IIIA, IIIB, and IIIC) – Cancer has spread to stomach muscle and 7-to-15 near lymph nodes; or spread to layer of stomach connective tissue (subserosa) and 3-to-6 near lymph nodes; or spread to layer of stomach connective tissue (subserosa) and 1-to-6 near lymph nodes; or spread to near organs, such as abdominal wall, adrenal gland, back of abdomen, colon, diaphragm, kidney, liver, small intestine, or pancreas. Cancer has spread to next layer of stomach (submucosa) or stomach muscle layer and 16 or more near lymph nodes; or spread to layer of stomach connective tissue (subserosa) or the stomach wall (serosa) and 7-to-15 near lymph nodes; or has spread to near organs, such as abdominal wall, adrenal gland, back of abdomen, colon, diaphragm, kidney, liver, small intestine, or pancreas and 1-to-6 near lymph nodes. Cancer has spread to layer of stomach connective tissue (subserosa) or stomach wall (serosa) and 16 or more near lymph nodes; or has spread to near organs, such as abdominal wall, adrenal gland, back of abdomen, colon, diaphragm, kidney, liver, small intestine, or pancreas and 7 or more near lymph nodes.
Stage IV – Cancer has spread to other parts of the body (distant metastasis), such as distant lymph nodes, the liver, lungs, or peritoneum (lining of abdomen).
While stomach cancer generally progresses slowly, the stage of stomach cancer determines its treatment and outcome (prognosis).
