A primary intracranial germinoma is associated with placenta-like alkaline phosphatase (PLAP) in the cerebrospinal fluid (CSF) and sometimes in the serum. PLAP (as well as c-kit) can also be demonstrated in the tumor by immunohistochemistry..
Significance: A pure germinoma (typically found in the pineal gland) is radiosensitive and can be treated without surgical resection.
The activity of PLAP is heat-resistant (does not show a major decline after heating).
In primary intracranial germinomas:
(1) The level of PLAP in the CSF prior to therapy is very high.
(2) The level decreases to normal with successful therapy.
(3) Recurrence of the tumor is associated with reappearance of the PLAP.
The presence of PLAP in the serum suggests more advanced disease. It may also be necessary to exclude metastasis to the CNS.
Causes for a false-negative result:
(1) very small primary tumor
(2) cystic tumor with intact cyst wall
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