Fig. 1

Illustration of an adult case presenting histologically as a low grade glioma (#12). This is an adult case of glioma (24 years at diagnosis) with FGFR3:TACC3 fusion with a low grade glioma (LGG) histological appearance initially and at recurrence. MRI at initial diagnosis showed a right frontal lesion with calcification and contrast enhancement (a). MRI at recurrence (b, c), showed an anterior high signal on FLAIR (c) without contrast enhancement (b). Histology at initial diagnosis (d, hematoxylin–phloxin–safron) and recurrence (e hematoxylin–phloxin–safron) showed an infiltrative and circumscribed growth pattern (f anti-neurofilamnet immunostaining), of an oligodendroglioma-like tumor with profuse microcalcifications (boxes) and without microvascular proliferation or tumoral necrosis. There was a strong and diffuse CD34 extra-vascular expression (g anti-CD34 immunostaining) and a strong and diffuse FGFR3 expression (h anti-FGFR3 immunostaining). No mitotic activity was observed and proliferation index was low (i anti-MIB1 immunostaining). Patient was simply monitored after surgeries and is still alive to date. Methylation class with v12.5 was ganglioglioma at both initial and recurrence with calibrated scores (CS) of respectively 0.41 and 0.61. Copy number variation (CNV) plots generated by the molecularneuropathology.org platform were the same between initial and recurrence (j). Gain of chromosome 7/loss of chromosome 10 was observed and there was mutation of TERT promotor. Scale bars: D, E: 50µm; F, G, H, I: 100 µm