Stomach cancer begins when cancer cells form in the inner lining of your stomach. These cells can grow into a tumor. Also called gastric cancer, the disease usually grows slowly over many years.
Scientists don’t know exactly what makes cancer cells start growing in the stomach. But they do know a few things that can raise your risk for the disease. One of them is infection with a common bacteria, H. pylori, which causes ulcers. Inflammation in your gut called gastritis, a certain type of long-lasting anemia called pernicious anemia, and growths in your stomach called polyps also can make you more likely to get cancer.