Leukemia is cancer of the blood cells. Most blood cells form in the bone marrow. In leukemia, cancerous blood cells form and crowd out the healthy blood cells in the bone marrow.The type of leukemia depends on the type of blood cell that has become cancerous.
Pepsin is an enzyme that breaks down proteins into smaller peptides (that is, a protease). It is produced in the stomach and is one of the main digestive enzymes in the digestive systems of humans and many other animals, where it helps digest the proteins in food.
Note that in both the stomach and the Pancreas the protein digesting enzymes are secreted in non-active forms-pepsinogen in the stomach and Tripsinogen and Chymotripsinogen in the pancreas. This is to prevent autodigestion.