What is the cause of stomach cancer?

Gastric cancer patients with black stool accompanied by a variety of forms, such as tarry soft stool, there may also be dry black particles of stool. And the color of the black edge is different, and the amount of blood loss. If the amount of bleeding is not much, below 300ml per day, stool is lighter black, if the amount of bleeding reaches 800ml, stool is soft, tarry dark stool.