Application of Comparative Genomic Hybridization, Spectral Karyotyping, and Microarray Analysis in the Identification of Subtype-Specific Patterns of Genomic Changes in Rhabdomyosarcoma

Rhabdomyosarcoma (RMS) in children occurs predominantly as two major histologically defined subtypes called embryonal RMS (RMS-E) and the prognostically less favorable alveolar RMS (RMS-A). Comparative genomic hybridization (CGH) was performed on 21 RMS and identified consistent gains affecting chromosomes 2 (8/10), 5 (5/10), 6 (3/10), 7 (7/10), 8 (9/10), 11 (6/ 10), and 12 (5/10) in RMS-E. Losses/deletions involved chromosomes 19 (2/10) and chromosomes 4, 9, 10, 17, 21 (1/10 each). High copy number amplification, involving the 2p24 region (5/11) and less frequently, the 12q13-21 (2/11), 9p22 (1/11), and 17q22-25 (1/11) regions, was detected in RMS-A. Gene amplification at band 2p24 was present in 6/12 alveolar tumors, and in each case, MYCN was amplified, together with the distally placed DDX1 gene. For these patients there was a shorter disease free interval and a higher mortality than patients with tumors without amplification. Detailed spectral karyotype analysis (SKY) was performed on two RMS cell lines (one of each subtype) and identified a surprisingly high level of structural change. Gene expression studies with the Atlas Human Cancer Array (588 genes) showed that 153 genes generated a signal of similar intensity in both cell lines, and 45 genes appeared to have subtype-specific expression. The chromosomal location of differentially expressed genes was compared to the pattern of genomic alteration in RMS as determined by CGH in this study and the literature.