The early symptoms of gastric cancer are similar to those of some gastrointestinal diseases such as gastritis, gastric ulcers, or duodenal ulcers. They don't have very specific clinical manifestations. Common symptoms include nausea, vomiting, discomfort or pain in the upper abdomen, and acid reflux-like symptoms, which are early symptoms in patients with gastric cancer. Therefore, when such symptoms appear, it is essential to seek medical attention promptly and undergo a thorough gastroscopy.