Our bodies are made up of tiny building blocks called cells. Normal cells grow and multiply when the body needs them. They die when they’re no longer needed. This is how balance is maintained. However, some cells go through a series of changes, called mutations in their DNA. These changes may cause the cells to grow out of control or not die when they should. Cancer occurs when cells multiply whether or not they’re needed. Cancerous cells are called malignant. In most cancers, the abnormal cells grow and form a lump called a tumor.
Stomach cancer, also called gastric cancer, is a disease in which cancer cells begin forming in the stomach. There are different types of stomach cancer. They grow in different parts of the stomach. The different types of cancer cells also look different under a microscope. The type of cancer you have determines your choices for treatment.
Most stomach cancers are of a type called adenocarcinoma. This type develops from the cells that form the innermost layer of the stomach, called the mucosa, in cells called epithelial cells.
These are other less common tumors found in the stomach:
Lymphomas. These are cancers of immune system tissue.
Gastrointestinal stromal tumors. These can be benign or cancerous. They form from a type of cell in the stomach wall called interstitial cells of Cajal.
Carcinoid tumors. These come from hormone-producing cells in the stomach.
These three types of cancer are rare and their treatment and prognosis (outlook) differ from adenocarcinomas.