It can continue to grow in size until it finally ruptures which spills out a vast amount of blood depending on the size of the rupture. This causes
acute internal hemorrhage. The affected dog
becomes acutely anemic because the dog's blood is free in the abdomen, in the case of the splenic tumor or free in the pericardium, in the case of a heart tumor, for instance, and not in blood vessels. The blood can then pour out of the mouth since it is not contained in blood vessels.