Figure 1. Spindle cell rhabdomyosarcoma with SRF-NCOA2 fusion.
This tumor is from a 7-month old child who presented with a posterior neck mass (case RMS2). (A) It is composed of monotonous spindle cells arranged in long fascicles, resembling leiomyosarcoma. The tumor infiltrates the adjacent fibroadipose tissue (original magnification 100×). By immunohistochemistry, it is diffusely positive for desmin (B) and multifocal nuclear positivity for myogenin (C). (D) Schematic representation of SRF-NCOA2 fusion involving exons 12 and 6, respectively. The numbers indicate exons. (E) This result was confirmed by RT-PCR which identified an in frame fusion of the SRF exon 6 with exon 12 of NCOA2, by direct sequencing of the 705 bp amplified product (F). FISH assay demonstrated break-apart signals for both SRF (G) and NCOA2 (H) (Probes centromeric to SRF and NCOA2 are in red, probes telomeric to SRF and NCOA2 are in green). (I) Number of reads normalized per million mapped nucleotides demonstrated differential expression of NCOA2 5′ and 3′ to the breakpoint, which supports the orientation of fusion transcript.