MYC DNA is structurally abnormal and MYC protein is overexpressed in MCL cells. (A) FISH was conducted using directly labeled dual-color break-apart Vysis MYC probes (5′ labeled in spectrum orange and 3′ in spectrum green), and images were captured using the Zeiss Axio Imager.Z2 Microscope with CytoVision Software. Magnification ×1000. (B) IHC staining in cell blocks from the 4 MCL cell lines and tonsil (bottom) as control. Moderately strong nuclear staining is seen in all 4 cell lines. In tonsil, most of small lymphoid cells including lymphocytes in mantle zone (MZ) and paracortical T-cell areas stain negative for MYC. Occasional large proliferative cells stain positive and are scattered within or outside the germinal centers (GC). The pattern is expected and shows specificity of the MYC immune stain. The dotted line denotes the border between the GC and the MZ. Magnification ×200.