A break in the lining of the lower part of the esophagus, the stomach, or the upper part of the small intestine. Peptic ulcers form when cells on the surface of the lining become inflamed and die. They are usually caused by Helicobacter pylori bacteria and by certain medicines, such as aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs). Peptic ulcers may be linked to cancer and other diseases.