Stomach cancer, also called gastric cancer, is a cancer that starts in the stomach. To understand stomach cancer, it helps to know about the normal structure and function of the stomach. The most common cause is infection by the bacterium Helicobacter pylori, which accounts for more than 60% of cases. Certain types of H. pylori have greater risks than others. Other common causes include eating pickled vegetables and smoking. Gastric cancers due to smoking mostly occur in the upper part of the stomach near the esophagus. Some studies show increased risk with alcohol consumption as well. Most of the time, stomach cancerdevelops through a number of stages over a number of years.