A, Fluorescence in situ hybridization performed on FFPE using a JAK2 specific break-apart probe set showing a split signal pattern, indicative of a JAK2 rearrangement. B, Large anaplastic cells with irregular and multilobated nuclei with occasional “hallmark” cells (H&E, 1000x, oil immersion); the anaplastic cells strongly and uniformly express CD30 (400x); the cells lack expression of ALK1 (400x); the anaplastic cells show strong expression of pSTAT3 (400x).