In terms of epidemiology, gastric cancer is not an infectious disease; the oncogenes or cancer cells cannot be transmitted to another person by any means, so gastric cancer is not contagious.
However, from an etiologic perspective, H. pylori, one of the main risk factors for the development of gastric cancer, can be transmitted from person to person, so gastric cancer can be “contagious” again. H. pylori can be transmitted from person to person through the oral-oral route (e.g., through saliva between mother and child or husband and wife), fecal-oral route (e.g., through contamination of water by the feces of an infected person), gastric-oral route (e.g., through gastroesophageal reflux or vomiting of stomach contents), and intra-family transmission (e.g., through close contact of family members or exposure to a common infectious agent). The oral-oral route is the main mode of transmission. Inadequate sterilization of endoscopes may also transmit H. pylori, i.e., medical-derived infection.