A cell will undergo changes that cause it to become cancerous. It will begin to grow and multiply uncontrollably. The cancer cells will form a tumor. The tumor will invade and destroy tissues around it as it grows. Eventually it can penetrate through the wall of the stomach and spread to structures around the stomach.
Cancer cells can also break off from the tumor and enter the blood stream.
These cells will form new tumors in other parts of the body, a process known as metastasis . Because the symptoms are vague and often ignored, stomach cancer can grow in the stomach for a long time before it is detected. The most common symptom is unexplained weight loss . People may complain of an uneasy sense of fullness, stomach heaviness, or distention. A person may also have chronic nausea and pain in the middle of the abdomen.