Core needle biopsy of mass. (a) 20× H&E section showing hypercellularity, and lacking any differentiated morphology. (b) and (c) Fluorescent photomicrographs showing biopsied tumor cells hybridized to commercial break-apart probes specific to the DDIT3 (b) and FUS (c) loci. Probes flank targeted gene sequence showing yellow signal when bound in proximity (intact locus) and showing individual red and or green signals when bound in isolation (rearranged locus). EWSR1 (not shown) was conversely intact with two paired (yellow) signals per nucleus.