Generally speaking, patients with early stage stomach cancer have no clinical symptoms, and without gastroscopy, it is more difficult to detect and produce obvious bad breath problems; patients with advanced stage stomach cancer often have rotten duck egg smell; however, not all patients with advanced stage stomach cancer have rotten duck egg smell bad breath, in addition, other unknown disease factors may also cause patients to have rotten duck egg smell bad breath, patients need to combine with clinical, to make a comprehensive judgment.