Cancer-related anemia: its causes and characteristics.

Under normal circumstances, the circulating red blood cell mass is maintained at a level that is constant in each individual, although that level may vary by more than 10% among individuals of the same age and gender. At normal ambient oxygen tension, two factors determine the circulating red blood cell mass: red blood cell life span, which is finite and in humans approximates 120 days; and the rate of effective red blood cell production. To maintain a constant red blood cell mass, therefore, approximately 20 mL of red blood cells must be produced each day to replace those red blood cells lost from the circulation through senescence. Anemia, which may be defined functionally as lack of sufficient red blood cells to maintain adequate tissue oxygenation, develops when the demand for new red blood cells exceeds the capacity of the bone marrow to produce them. This may be due to excessive red blood cell destruction, impaired red blood cell production, bleeding, or any combination of these. Acquired anemia is always a consequence of another disorder, which must be identified to ensure that the corrective therapy is appropriate. In patients with solid tumors, multiple mechanisms for causing anemia have been identified: blood loss that is either intrinsic or iatrogenic; nutritional deficiencies involving primarily iron or folic acid; hemolysis (autoimmune, traumatic, or drug-induced); bone marrow failure due to tumor encroachment, myelofibrosis, or marrow necrosis; infection; inflammation; or simply the presence of a cancer elsewhere in the body. The three noted causes of marrow failure share a common denominator: impaired production of erythropoietin. For any degree of anemia, a patient with cancer produces much less erythropoietin than expected and, therefore, cannot compensate for impaired red blood cell production. Inflammation or infection can exacerbate this situation. Indeed, anemia in patients with cancer appears to behave much like that in patients with chronic renal failure who become anemic because of the inability of the kidneys to produce erythropoietin adequately. The cause of impaired erythropoietin production in patients with cancer who have anemia is not entirely understood, but may be due in part to the production of inflammatory cytokines in response to the tumor. Such cytokines also would be expected to blunt the ability of the bone marrow to respond to the available circulating erythropoietin.(ABSTRACT TRUNCATED AT 400 WORDS)