Apheresis, most commonly used in the treatment of leukemia and lymphoma patients, is a process used to obtain peripheral blood stem cells for transplantation. Blood is collected from the patient; part of the blood, such as platelets or white blood cells, is removed by a machine; and the rest of the blood is returned to the donor. The collected cells may be treated with drugs to destroy cancer cells before being frozen until they are transplanted back to the patient.