Blood cells are produced in the bone marrow. The three main components of blood are red blood cells, which carry oxygen; white blood cells or leukocytes, which fight infection; and platelets, also called thrombocytes, which assist in the formation of blood clots.

When a blood vessel is damaged, platelets adhere to the surface of the damaged vessel and release chemicals. These chemicals attract more platelets, as well as red blood cells, in order to form a clot, or thrombus. As the clot grows, the blood vessel narrows, thereby decreasing blood loss. This process is called coagulation.

Normal platelet counts are in the range of 150,000 to 350,000 platelets per microliter. Thrombocytopenia is a disorder in which there are not enough platelets. When the platelet count is decreased, the body is unable to form blood clots and, therefore, is unable to control bleeding.

Bruising and bleeding can occur from relatively little trauma. When the platelet count gets below 10,000 platelets per microliter, bleeding can develop without trauma.

Chemotherapy-induced thrombocytopenia is a disorder that develops as an adverse effect of chemotherapy. Cancer drugs not only kill cancer cells, they can also damage the platelet-forming cells in the bone marrow.

The severity of this disorder depends on the type of chemotherapy and the duration of treatment. Fortunately, chemotherapy-induced thrombocytopenia can be managed with platelet transfusions, additional medications, such as blood cell growth factors, or with blood stem cell transplants.