Comparative expressed sequence hybridization (CESH) is an expression profiling technique which identifies chromosomal regions corresponding to differential gene expression. Here, we observe that various tumor samples including rhabdomyosarcoma show very prominent staining on the short arms of the acrocentric chromosomes suggesting an increase in expression of ribosomal RNA synthesized from the repetitive rDNA of the nucleolar organizer regions located on these chromosomes. Survival analysis showed a correlation with overexpression from this region and a poor prognosis in rhabdomyosarcoma. This phenomenon was studied in an extended set of rhabdomyosarcoma tumor samples using quantitative real-time reverse transcriptase-PCR to quantify levels of pre-rRNA (precursor ribosomal RNA). It was demonstrated first that the strong CESH signals did correspond to a marked increase in pre-rRNA expression and second that high pre-rRNA expression correlated with an adverse prognosis in alveolar subtype rhabdomyosarcoma. In addition, we demonstrate that pre-rRNA expression is significantly correlated with tumor stage. We conclude that measuring expression of pre-rRNA by real-time PCR is a useful prognostic marker in alveolar rhabdomyosarcoma. Furthermore, given that we have observed similar rDNA staining in all cancer types that we have studied by CESH, we propose that pre-rRNA overexpression is a general phenomenon in cancer and that our real-time PCR assay may be applicable as a prognostic marker in other tumor types.
(c) 2006 Wiley-Liss, Inc.