Three enolase isozymes (αα, αγ, and γγ) and S-100 protein in the extract of neuroendocrine tumors (neuroblastoma, ganglioneuroblastoma, ganglioneuroma, and pheochromocytoma) and nonneuroendocrine tumors (Wilms' tumor, rhabdomyosarcoma, and hepatoblastoma) were determined by means of enzyme immunoassay systems.

All of the tumors examined showed a high level of αα-enolase (1.71 to 19.0 µg/mg protein). Levels of nervous system-specific enolases (NSE; αγ and γγ) in the neuroendocrine tumors were also rather high (αγ, 1.64 to 7.45 µg/mg protein; γγ, 0.052 to 5.56 µg/mg protein). However, the NSE concentration in the extract of nonneuroendocrine tumors was low (αγ, < 0.88 µg/mg protein; γγ, 0 µg/mg protein). The level of S-100 protein was relatively high in ganglioneuroma (>500 ng/mg protein) and ganglioneuroblastoma (>100 ng/mg protein), but low in neuroblastoma (less differentiated neuroendocrine tumor) and nonneuroendocrine tumors.

Serum levels of enolase isozymes were also determined in neuroblastoma patients before and after resection of primary tumor or effective chemotherapy. The elevated level of serum NSE (αγ and γγ) was markedly decreased with little change in the αα level by the treatment.

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