Dual-color, break-apart fluorescent in situ hybridization was performed to confirm the ALK expression. The centromeric (green) and telomeric (red) fland the ALK locus. Splitting of the red and green signals indicates ALK rearrangement. A: No EML4-ALK rearrangement. B, C and D: EML4-ALK rearrangements. A break-apart signal pattern, where one fusion signal and a single red and green signal pattern was observed in most nuclei (B and C). A few nuclei showed a predominant signal pattern of deletion of the 5’region (D).