Functional iron deficiency anemia in patients with cancer.

Anemia is frequently observed in patients with cancer owing to anticancer chemotherapy, radiation therapy, and inflammatory responses. This often leads to functional iron deficiency, characterized by adequate iron stores but impaired use of iron for red blood cell production. This condition, termed functional iron deficiency anemia (IDA), is identified by a ferritin level of 30-500 µg/dL and a transferrin saturation < 50%. Functional iron deficiency often develops with the prolonged use of erythropoiesis-stimulating agents, leading to a diminished response to anemia treatment. Although oral iron supplementation is common, intravenous iron is more effective and recommended in such cases. Recent studies have shown that ferric carboxymaltose (FCM) is effective in treating functional IDA in patients with cancer. However, because of its potential to induce asymptomatic severe phosphate deficiency, it is important to closely monitor phosphate levels in patients receiving FCM.