Figure 1.

Radiologic and histopathologic findings on initial presentation and biopsy. (A): Postcontrast T1‐weighted magnetic resonance images show a contrast‐enhancing tumor centered in the left frontal lobe and involving the corpus callosum (white arrowheads). Top: axial; middle: coronal; bottom: sagittal. (B): H&E‐stained slides from the initial biopsy show a hypercellular, pleomorphic neoplasm with microvascular proliferation (top right; black arrowheads). By immunohistochemistry, the neoplastic cells are positive for OLIG2 (middle left) and negative for R132H‐mutant IDH (middle right; wild‐type pattern). Fluorescence in situ hybridization using green and red NTRK2‐specific break‐apart probes flanking the breakpoint (bottom row) shows split red and green signals (white brackets: split signals, white arrowheads: nonsplit signals), confirming NTRK translocation. Abbreviations: IDH, isocitrate dehydrogenase; NTRK, neurotrophic receptor tyrosine kinase.