IRON OVERLOAD FOLLOWING HEMATOPOIETIC STEM CELL TRANSPLANTATION: PREVALENCE, SEVERITY AND MANAGEMENT IN CHILDREN AND ADOLESCENTS WITH MALIGNANT AND NON-MALIGNANT DISEASES

Background: Iron overload (IOL) is a frequently reported complication following hematopoietic stem cell transplantation (HSCT) which has been extensively assessed in the field of hemoglobinopathies, but has not been thoroughly characterized after HSCT in pediatric malignancies. Objectives: Our aim was to assess prevalence, severity, risk factors and management of IOL, as defined by means of biochemical (serum ferritin) and radiological tools (T2*-MRI), in a cohort of pediatric patients transplanted for either malignant or benign diseases. Study design: Monocentric, retrospective, observational study. All the 163 patients alive and in continuous remission 24 months after HSCT, out of the 219 consecutive children and adolescents transplanted at our Institution between 2012 and 2018, were included in the study. IOL was classified into four categories, i.e. absent, mild, moderate and severe. Results: Of the 163 patients, 73% had some degree of IOL, which was mild, moderate and severe in 37%, 29% and 7%, respectively. Moderate/severe IOL was more frequent among patients diagnosed with a malignant versus benign disease (43% vs 19%; p 0.0065). Ferritin trend lines showed a "bell-shaped" distribution, with the highest levels being recorded during the first 6 months after HSCT, followed by a spontaneous reduction. Both pre-HSCT (1659 versus 617 ng/mL, p<0.001) and maximum post-HSCT (2473 ng/mL versus 1591 ng/mL, p<0.001) median ferritin levels were statistically higher among patients with malignancies. Radiological assessment of IOL confirmed a more severe degree in malignant compared to benign disorders (median T2*-MRI 4.20 msec, IQ: 3.0-6.40 versus 7.40, IQ: 4.90-11.00, respectively - p 0.008). T2* levels were associated with the number of transfusions performed (p 0.0006), with a steeper drop in T2* values for the first 20 transfusions and a milder slope subsequently. T2* and ferritin values showed a statistically significant negative exponential relationship (p<0.0001), though ferritin levels ≥1000 ng/mL showed a poor specificity (48%) and positive predictive value (53%) in discriminating moderate-to-severe from absent-mild IOL as assessed by T2*-MRI, but high sensitivity (92%) and negative predictive value (91%). In a multivariable model, >20 transfusions (OR 4.07, 95% CI 1.61-10.68, p 0.003) and higher pre-HSCT ferritin levels (p<0.001) were associated with the risk of developing moderate-to-severe IOL. A sibling donor (OR 0.29, 95% CI 0.10-0.77, p 0.015) and a non-malignancy (OR 0.27, 95% CI 0.08-0.82, p 0.026) were protective factors. Phlebotomies (66%), low-dose oral chelators (9%) or a combined approach (25%) were started at a median of 12 months after HSCT in 78% of the patients with IOL. Six% of the patients treated exclusively with phlebotomies (median 14, significantly higher in patients >40 kg) discontinued them due to poor venous accesses, lack of compliance or hypotension, whereas 39% of patients treated with chelators developed mild renal or hepatic side effects which resolved upon tapering or discontinuation. Conclusions: Patients with malignancies showed statistically higher pre- and post-HSCT ferritin levels and lower T2*. High ferritin recorded upon T2*-MRI showed unsatisfactory diagnostic accuracy in predicting IOL, thus, T2*-MRI should be regarded as a key element to confirm IOL after HSCT in patients with elevated ferritin levels. IOL treatment is feasible after HSCT.