Fig. 1: Ferritin in serum and resected tumour tissue of GBM and meningioma patients.

a Based on SF quantification, patients were assigned to two cohorts: the RefR cohort (open boxes) showing SF levels inside the reference range (i.e. below the 95th percentile) of the TINA-Quant ferritin assay and the ExtR cohort (black boxes) with SF levels elevated above the 95th percentile. Dotted lines refer to the median reference levels reported for healthy male and female donors.³ Note that only a minority of GBM patients (ExtR cohort) showed very high SF levels (462–1355 ng/ml; median = 727 ng/mL), which is in line with existing data, with only 4 of a total of 57 glioma patients investigated so far, showing extremely high SF levels (Supplemental Table 1). Meningioma patients showed lower SF levels, which is significant (p > 0.05) for the RefR cohorts, and the highest SF value observed in meningioma patients (766 ng/mL) locates close to the median SF level of GBM–ExtR patients. b Immunohistochemistry of resected GBM and meningioma tissue evaluated by the labelling index (i.e. the percentage of immune-positive cells) demonstrates a significantly (p < 0.005) higher immunoreactivity for ferritin in GBM samples. In both types of tumour specimens, labelling for the FTL subunit was significantly (p < 0.05; p < 0.005) higher compared with FTH. c In GBM tissue, no differences of ferritin labelling were found between samples obtained from the RefR and ExtR cohort, the highest FTL labelling being observed in RefR cohort samples: 328 ng/mL (upper dot) and 206 ng/mL (lower dot). *p < 0.05; **p < 0.005 compared with the healthy reference population in (a) (Wilcoxon sign test for median difference based on gender-specific SF values) or as indicated (Mann–Whitney U exact test for independent samples for the comparison between the two patient cohorts in (a, c), and Wilcoxon signed-rank test for paired samples in b); ⁺p < 0.05; ⁺⁺p < 0.005 compared with meningioma patients (Mann–Whitney U exact test for independent samples). The dots in meningioma RefR cohort (a) and (b) highlight statistical outliers. N refers to the number of investigated patients (a) or tumour specimens (b).