Bone marrow suppression is a decrease in the activity of blood cell precursors in the bone marrow, resulting in a decrease in peripheral blood cells. Both red and white blood cells in the bloodstream originate from stem cells in the bone marrow. The blood cells in the blood stream are short-lived and often require constant replenishment. In order to achieve timely replenishment, stem cells, which are the precursors of blood cells, must divide rapidly. Chemotherapy and radiation, as well as many other antitumor treatments, target rapidly dividing cells and thus often result in the suppression of normal bone marrow cells. Adverse effects of tumor therapy, such as causing anemia and leading to decreased resistance to infection, are the effects of tumor therapy on bone marrow cells.