Sensitive detection of rare circulating neuroblastoma cells by the reverse transcriptase-polymerase chain reaction

The presence of circulating tumor cells in patients with localized or disseminated neuroblastoma may be a significant prognostic factor at diagnosis and may antedate the detection of relapse by other diagnostic studies. We report the development of a highly sensitive detection assay for circulating neuroblasts based on the reverse transcriptase-polymerase chain reaction (RT-PCR), using the neuroendocrine protein gene product 9.5 (PGP 9.5) as the tumor marker. Analysis of RT-PCR products by agarose gel electrophoresis demonstrated that neuroblastoma cell lines were uniformly positive, whereas peripheral blood mononuclear cells were negative. Alkaline Southern blotting with a PGP 9.5-specific probe revealed scant expression of PGP 9.5 in peripheral blood mononuclear cells, well below the limits of detection by electrophoresis alone. The system was able to detect a single neuroblastoma cell in 10(7) peripheral blood mononuclear cells. Eighteen patient samples were analyzed by PGP 9.5 RT-PCR and the results compared with immunocytology in 16. Ten of the 18 were negative by both studies. Eight of the 18 were positive by PGP 9.5 RT-PCR, 4 of which were also positive by immunocytology. PGP 9.5 RT-PCR was able to detect circulating neuroblasts in two patients with negative immunocytology, the first with progressive bone marrow disease and the second at high risk for relapse but no other evidence of disease. PGP 9.5 RT-PCR allows the detection of circulating neuroblastoma cells with a sensitivity greater than immunocytology. It will be useful in evaluating the clinical significance of circulating tumor cells with respect to prognosis and early detection of relapse, and in the screening of peripheral stem cell harvests prior to autologous infusion.