Purpose: The purpose of this study was to establish a sensitive and semiquantitativemethod for the detection of minimal residual diseaseof neuroblastoma, the most common solid tumor in childhood.

Experimental Design: Analysis was performed on a molecular level by reverse transcription-PCR using a new, real-time detection method. We measured two genes simultaneously, tyrosine hydroxylase (TH) as the target gene and glyceraldehyde-3-phosphate dehydrogenase as a reference gene, in blood and bone marrow samples at diagnosis and after follow-up from six patients with neuroblastoma, one patient with ganglioneuroma, and one patient with ganglioneuroblastoma.

Results: The sensitivity of the assay was 1:10⁶ peripheral WBCs. Four patients with stage IV neuroblastoma and one patient with stage III neuroblastoma were scored positive. The other stage III patient and the other two patients with ganglioneuroma and ganglioneuroblastoma followed by acute lymphoblastic leukemia, respectively, were scored negative. Control bone marrow aspirates were also negative. The TH assay is more sensitive than immunohistochemical detection, and the results of the TH assay corresponded with the results of MYCN amplification.

Conclusions: The described TH assay is specific, sensitive, and semiquantitative and can be used for the detection of neuroblastoma cell involvement in bone marrow and blood at diagnosis and during therapy. Furthermore, the TH assay is a possible prognostic marker for neuroblastoma.