Myelosuppression is a decrease in the production of blood cells. Normal blood contains large numbers of cells, including red blood cells to carry oxygen and white blood cells to fight infections. The blood also contains platelets, tiny cell fragments that initiate blood clotting. These cells and fragments are made in the bone marrow, a reddish substance found in the centers of some bones. Healthy bone marrow makes large numbers of red blood cells, white blood cells, and platelets each day to replace those that wear out. In myelosuppression, the bone marrow makes too few of these cells.
A decrease in the number of red blood cells, called anemia , is very common in cancer patients. A drop in white blood cell numbers is often a problem during chemotherapy . One type of white blood cell, called a neutrophil, is usually affected most severely. A decrease in these cells is called neutropenia . Because neutrophils are responsible for defending the body against bacteria, neutropenia increases the chance of an infection. Thrombocytopenia , a drop in the number of platelets in the blood, is more rare; platelet numbers become low enough to cause problems in less than 10% of cancer patients.