With GI cancer is also called gastric cancer or stomach cancer. Cancer cells grow out of control in your stomach. Cancer can form anywhere in your stomach. Most cases of stomach cancer involve abnormal cell growth in the place where your stomach meets your esophagus (gastroesophageal junction) and in the main part of your stomach.
About 95% of the time, stomach cancer starts in your stomach lining and progresses slowly. Untreated, it can form a mass (tumor) and grow deeper into your stomach walls. The tumor may spread to nearby organs like your liver and pancreas.