The early signs of gastric cancer may include nausea, vomiting, or mild acid reflux, which are symptoms similar to those of gastritis, stomach ulcers, or duodenal ulcers. Therefore, initially, these patients may not take their condition seriously, assuming they might just have gastritis or peptic ulcers. These are some of the early manifestations of gastric cancer, and some patients may also experience discomfort and a feeling of fullness after eating.