Stomach ulcer, gross specimen. Gastric (peptic) ulcers are caused by excessive acid secretion that erodes the mucus protecting the stomach lining. The most common cause for such damage is due to infection with the bacterium Helicobacter pylori. This thinning of the mucus may result in inflammation (gastritis) or local erosion of the stomach lining (an ulcer). The ulcer (centre) is sharply defined and contains tissue debris and inflammatory secretions. A severe, untreated ulcer can sometimes perforate the stomach wall, allowing digestive juices to leach into the abdominal cavity. Treatment of a perforated ulcer would generally require immediate surgery.