Stomach cancer is often diagnosed at an advanced stage because symptoms rarely show at the start but frequent heartburn may be a sign of cancer which is also known as gastric cancer. According to Express.co.uk stomach cancer is often diagnosed at an advanced stage because symptoms can be rarely comprehended at the start. Other symptoms to watch out for include a painful tummy or sternum feeling full after eating small amounts of food and a burning sensation when swallowing. Finding blood in your stool persistent indigestion and feeling constantly out of breath are also signs of the condition. Men smokers