5145 Introduction and aims: Iron deficiency as a major component in the pathogenesis of anemia in cancer is not acknowledged by most oncologists, possibly except when arising from GI blood loss. Iron deficiency is associated with clinical symptoms such as cognitive impairment, fatigue, and reduced exercise performance. New iron formulations are available that allow rapid iron supplementation with single infusions. This treatment could ameliorate symptoms of iron deficiency and correct anemia. Here, we studied iron parameters and their correlation with erythropoiesis and inflammatory markers in a large unselected cohort of patients with cancer. In addition, we investigated the suitability of serum ferritin and transferrin saturation (TSAT) as parameter for assessment of the iron status. Patients and methods: Data from 1627 patients (median age: 66.4 years, range: 20–97 years) presenting sequentially at the Center for Oncology and Hematology, Wilhelminenspital, Vienna between October 01, 2009 and January 26, 2010, have retrospectively been analyzed. Patients were at different stages of their disease or may not have had an established diagnosis at the time of testing. In patients with multiple testing during this period only the first sample taken was included. TSAT (n=1516), serum ferritin (n=887), serum iron, CRP, and complete blood count, were determined by using standard techniques. Commonly used definitions for absolute iron deficiency (AID), [TSAT <20% and serum ferritin <30ng/ml, in case serum ferritin was not available TSAT <10%] and for functional iron deficiency (FID), [TSAT <20% and serum ferritin ≥30ng/ml, in case serum ferritin was not available TSAT between 10 and 20%] have been applied. Fisher's exact test was used for comparison of frequencies and Pearson's product moment correlation coefficient for evaluation of correlation. Results: Table 1 shows the distribution of TSAT and serum ferritin categories in 1627 patients with cancer. AID was found in 116 patients (7.7%) of the 1516 patients for whom TSAT was available. Eighty-three (72%) of the AID patients presented with anemia (defined by hemoglobin <12g/dl). AID was most common in patients with colorectal and pancreatic cancer (12% and 11%, respectively), and not present in patients with testicular and prostate cancer (p=0.013). FID was diagnosed in 530 patients (35%) and 222 (42%) of them were found to be also anemic. Multivariate analysis revealed a statistically significant correlation between TSAT and serum ferritin (R=0.286, p<0.001), serum iron (R=0.874, p<0.001), hemoglobin (R=0.201, p<0.001) and CRP (R=-0.205, p<0.001) (figure 1). Serum ferritin, in contrast, did not correlate with serum iron (R=0.051, p=0.132), but correlated with hemoglobin (R=-0.259, p<0.001), TSAT (R=0.286, p<0.001), and CRP (R=0.396, p<0.001). Conclusion: AID (7.7%) and even more so FID (35%) are frequent co-morbidities in patients with various types of cancer. Seventy-two percent of patients with AID and 42% with FID presented with overt anemia. TSAT correlated closely with serum iron and hemoglobin levels and seems to be the preferred parameter for assessment of iron status in patients with chronic diseases often complicated by increased inflammation. Serum ferritin was found to be an inadequate parameter for assessment and monitoring of iron status. As iron deficiency has been linked with various symptoms, the question arises whether iron supplementation would benefit patients with FID without overt anemia. Future studies should evaluate the role of novel intravenous iron preparations in ameliorating the symptoms of iron deficiency with or without anemia. Disclosures: Klement: Vifor Pharma Ltd: Employment. Cushway:Vifor Pharma Ltd.: Employment.

SummaryFerric carboxymaltose (FCM) administration helps reduce transfusion requirements in the perioperative situation, which improves patient outcomes and reduces healthcare costs. However, there is increasing evidence of hypophosphataemia after FCM use. We aim to determine the incidence of hypophosphataemia after FCM administration and elucidate potential biochemical factors associated with the development of subsequent hypophosphataemia. A retrospective review of anonymised data of all FCM administrations in a single institution was conducted from August 2018 to August 2021. Each unique FCM dose administered was examined to assess its effect on Hb and serum phosphate levels within the subsequent 28 days from each FCM administration. Phosphate levels were repeatedly measured within the 28‐day interval and the lowest phosphate level within that period was determined. Patients' serum phosphate levels within 28 days of FCM administration were compared against normal serum phosphate levels within 2 weeks before FCM administration. The odds ratios of various pre‐FCM serum markers were calculated to elucidate potential biochemical predictors of post‐FCM hypophosphataemia. In 3 years, a total of 1296 doses of FCM were administered to 1069 patients. The mean improvement in Hb was 2.45 g/dL (SD = 1.94) within 28 days of FCM administration, with the mean time taken to peak Hb levels being 6.3 days (SD = 8.63), which is earlier than expected, but was observed in this study and hence reported. The incidence of hypophosphataemia <0.8 mmol/L was 22.7% (n = 186), and <0.4 mmol/L was 1.6% (n = 9). This figure is lower than the numbers reported in previously published meta‐analyses given that routine checks of serum phosphate levels were not conducted initially and hence could possibly be higher. The odds of developing hypophosphataemia (<0.8 mmol/L) were 27.7 (CI: 17.3–44.2, p < 0.0001) if baseline serum phosphate was less than 1 mmol/L. The odds of developing hypophosphataemia (<0.8 mmol/L) were 1.3 (CI: 1.08–1.59, p < 0.01) if the change in Hb levels observed after FCM administration were more than 4 g/dL. Hypophosphataemia after FCM administration is significant and FCM should be used by clinicians with caution.