Expression of protein gene product 9.5 and tyrosine hydroxylase in childhood small round cell tumors.

Small round cell tumors of childhood can be histologically ambiguous, can require tumor markers for an accurate diagnosis, and include neuroblastoma, peripheral primitive neuroectodermal tumor (pPNET), Ewing's sarcoma (ES), lymphoma, and rhabdomyosarcoma. Because the cell type of origin for ES remains controversial, characterizing gene expression in ES can provide diagnostic markers and lead to better understanding of tumor biology. We studied RNA expression of the neuronal genes protein gene product 9.5 (PGP 9.5) and tyrosine hydroxylase (TH) by Northern analysis in cell lines and tissue from small round cell tumors. PGP 9.5 showed strong expression in 17 of 17 neuroblastoma cell lines, 9 of 9 pPNET cell lines, and 11 of 11 ES cell lines. PGP 9.5 was weakly expressed in 1 of 1 alveolar rhabdomyosarcoma cell lines but not in 1 of 1 embryonal rhabdomyosarcomas, and weak expression was seen in 1 of 7 leukemia cell lines. In tumor tissue, all 12 neuroblastomas expressed PGP 9.5, as did all 7 pPNET and all 7 ES. PGP 9.5 was very weakly expressed in 6 of 9 rhabdomyosarcomas and 1 of 9 lymphomas. TH was expressed only in neuroblastomas, and no TH expression was seen in cell lines or tissue from other tumors. As high expression of PGP 9.5 was only found in neural tumors; PGP 9.5 expression by ES provides further evidence for a neural origin of this tumor, whereas TH expression is highly specific for neuroblastomas. PGP 9.5 expression should allow sensitive detection of minimal residual disease for ES and pPNET using reverse transcription-PCR, and the variability in TH and PGP 9.5 expression levels in neuroblastomas indicates that expression of both genes should be used for monitoring minimal residual disease by reverse transcription-PCR.