Stomach cancer (gastric cancer) starts when cancer cells form in the stomach lining. Early symptoms can include indigestion and heartburn, a bloated feeling after eating a meal, heartburn, slight nausea and loss of appetite. More serious symptoms often appear as a stomach tumor grows, including stomach pain, blood in the stool, vomiting, unintended weight loss and trouble swallowing. Inflammation in the gut (gastritis), anemia and stomach growths (polyps) can increase the risk of stomach cancer.