The stomach is opened here to reveal a gastric adenocarcinoma In the U.S., most gastric cancers are discovered at a late stage when the neoplasm has invaded and/or metastasized. In Japan, where the incidence of gastric cancer is high, endoscopic screening is conducted, and more cancers are detected at an early stage. ALL gastric ulcers and ALL gastric masses must be biopsied, because it is not possible to tell from gross appearance alone which are benign and which are malignant. In contrast, virtually all duodenal peptic ulcers are benign.