FISH analysis. (A-B) Interphase FISH analyses in cHL with a IGH-BCL3 fusion. (A) The large Hodgkin cell nucleus on the right shows multiple splits of BCL3 break-apart probe, whereas the small cell on the left shows the normal signal pattern for 2 intact BCL3 loci (ie, 2 colocalized signals). (B) Multiple colocalizations of IGH-telomeric (green) and IGH-centromeric (red) probes with a BCL3 spanning probe (pale blue; arrows) confirming IGH-BCL3 juxtaposition in an HRS nucleus of the same case. (C-D) Metaphase FISH analyses in PTCL. (C) Split of the TCRAD break-apart probe indicating a TCRAD breakpoint and concomitant loss of the normal TCRAD allele. The yellow arrow points to the chromosome containing a TCRAD centromeric signal (red), whereas white arrows point to marker chromosomes containing TCRAD telomeric signals (green). (D) Extra red signal for the BCL3 telomeric probe (yellow arrow) and residual red signals colocalizing with the green BCL3 centromeric signal (white arrows), indicating a chromosomal breakpoint slightly telomeric to the BCL3 gene. The yellow and white arrows in panels C and D correspond to the same marker chromosomes, respectively. Images were acquired using a 63 ×/1.40 numeric aperture oil objective in a Zeiss Axioskop2 fluorescence microscope (Zeiss, Göttingen, Germany) equipped with the appropriate filter sets (AHF, Tübingen, Germany) and documented using the ISIS imaging system (MetaSystems, Altlussheim, Germany).