Causes

It's not clear what causes stomach cancer, though research has identified many factors that can increase the risk.

Doctors know that stomach cancer begins when a cell in the stomach develops changes in its DNA. A cell's DNA contains the instructions that tell the cell what to do. The changes tell the cell to grow quickly and to continue living when healthy cells would die. The accumulating cells form a tumor that can invade and destroy healthy tissue. With time, cells can break off and spread (metastasize) to other areas of the body.