Stomach cancer, or gastric cancer, refers to cancer arising from the inner layer (the "epithelium") of the stomach. Cancers arising from the stromal elements (such as gastro-intestinal stromal tumor (GIST) or from the mucosal associated lymphoid tissue (MALT) are completely different entities, and not included in the usual understanding of the term "gastric cancer."

Stomach cancer causes over 700,000 deaths worldwide per year. Outcomes are often poor with a less than 10% 5-year survival rate, largely because most people with the condition present with advanced disease.