A Highly Sensitive and Specific Chemiluminescent Enzyme Immunoassay for Placental Alkaline Phosphatase in the Cerebrospinal Fluid of Patients with Intracranial Germinomas

<b><i>Background:</i></b> Placental alkaline phosphatase (PLAP) in cerebrospinal fluid (CSF) has been proposed as a tumor marker for intracranial germinomas. The purpose of the present study was to develop a sensitive assay for measuring CSF PLAP and to evaluate the clinical significance of PLAP in patients with germinomas. <b><i>Methods:</i></b> A chemiluminescent enzyme assay for PLAP was developed using an anti-human-PLAP monoclonal antibody. PLAP concentrations were determined in 37 controls, 36 germinomas, 3 nongerminomatous germ cell tumors, 21 gliomas and 12 other brain tumors. <b><i>Results:</i></b> The assay detection limit was 5 pg/ml. The median PLAP concentration in the control group was below the detection limit. Significantly higher PLAP levels were detected in all 36 germinoma patients, with values ranging from 16 to 3,700 pg/ml. The high PLAP concentrations of 17 germinoma patients decreased to below the detection limit after complete remission had been achieved with radiochemotherapy. The sensitivity and specificity of PLAP for germinomas were 94 and 97%, respectively, with a cutoff value of 30 pg/ml. <b><i>Conclusions:</i></b> The results of this study suggest that the determination of CSF PLAP by the chemiluminescent method described here provides a clinically useful tumor marker for the diagnosis and monitoring of intracranial germinomas.