High-Dose Intravenous Ferric Carboxymaltose/Derisomaltose Without ESAs for Cancer-Related Anemia in Japan: A Retrospective Single-Center Cohort Study

Background/Objectives: In Japan, cancer-related anemia (CRA) is common, and erythropoiesis-stimulating agents (ESAs) are not approved for chemotherapy-induced anemia. Modern intravenous (IV) iron formulations, such as ferric carboxymaltose (FCM) and ferric derisomaltose (FDI), enable high-dose repletion; however, real-world evidence in ESA-free oncology settings remains limited. Methods: This single-center retrospective study included patients with CRA (N = 55) who received high-dose IV iron (FCM or FDI). Iron phenotypes were classified as absolute iron deficiency (ID), functional ID, or non-ID. The primary endpoint was hemoglobin (Hb) change from baseline to approximately 1 month (21–45 days) in the non-transfused patients. Secondary endpoints included responder rate (ΔHb ≥ 1.0 g/dL), transfusion avoidance rate, dosing adequacy relative to Ganzoni-calculated iron deficit, and safety, particularly hypophosphatemia. Results: Among the non-transfused patients, mean Hb increased from 8.76 ± 1.34 g/dL to 9.73 ± 1.75 g/dL (mean ΔHb +0.92 ± 1.44 g/dL; p < 0.001). The responder and transfusion avoidance rates were 48.9% and 81.8%, respectively. Functional ID was most prevalent (52.7%), with clinically meaningful Hb responses. A total of 38.2% achieved approximately 1000 mg dosing. The safety profile was excellent, and no infusion reactions or symptomatic hypophosphatemia was observed (median serum phosphate changed from 3.4 [3.0–3.9] to 3.2 [2.7–3.8] mg/dL). Conclusions: In this real-world Japanese oncology setting where ESAs were not available for chemotherapy-induced anemia, high-dose IV iron monotherapy (FCM or FDI) was well tolerated and was associated with modest short-term Hb increases and a high observed rate of transfusion avoidance within a 21–45-day assessment window. These findings suggest that a proactive, TSAT-guided IV iron therapy approach may be a pragmatic option for selected patients; however, durability beyond 1 month, optimal re-dosing, and generalizability require confirmation in larger, longer prospective studies.