Germinoma laboratory tests

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: {{Simrat}

Laboratory Findings

The following tests are done for intracranial germ cell tumors:

• CSF cytology to detect malignant cells
• Measurement of AFP and beta-hCG in the CSF and serum
  • Tumor marker levels are usually higher in CSF than in serum. In patients in whom endoscopic biopsy is not considered possible, detection of elevated tumor markers may be sufficient for diagnosis.
  • Measurement of beta-hCG and AFP in the CSF is more sensitive than serum levels in detecting abnormalities. However, due to discordant serum and CSF tumor marker results that were observed, both serum and CSF tumor markers should be obtained in the absence of clinical contraindications. Lumbar CSF is considered more accurate for tumor markers and cytology than ventricular CSF.
  • Tumor markers from ventricular CSF can be used , if a lumbar puncture is contradicted.
• Laboratory studies to detect the hormonal dysfunction that may occur in patients with central nervous system (CNS) germinomas are as follows:
  • Diabetes insipidus
    • Serum sodium, serum osmolality, and urine osmolality
  • Hypopituitarism
    • Thyroid function tests, growth hormone levels, cortisol levels
  • Gonadal dysfunction
    • Testosterone level in males; prolactin level in females

Although elevated alpha-fetoprotein levels may be seen in the germ cell tumors; however, AFP levels may be normally elevated both in serum and CSF of neonates and infants. Alpha-fetoprotein (AFP) levels may be elevated in the following tumors:

• Pure endodermal sinus tumor (yolk sac)
• Embryonal carcinoma
• Malignant teratoma.

Interpretation of the AFP level must take into account the normal variation seen in this age group. The median AFP levels in CSF, in normal infants, are as follows:

Age	AFP levels
≤31 days	61 kIU/L
32-110 days	1.2 kIU/L
8-12 months	Adult levels

Other relevant tumor marker findings are as follows:

Level of tumor marker	interpretation
beta human chorionic gonadotropin (β-hCG) above 50-100 IU/L	choriocarcinoma
lower levels of β-hCG	pure germinoma that contain syncytotrophoblastic giant cells
Basal ganglia, thalamus, cerebral hemisphere	5-10%
Both pineal and suprasellar region	6-13%

Levels of beta human chorionic gonadotropin (β-hCG) above 50-100 IU/L indicate the presence of choriocarcinoma while lower levels may indicate pure germinoma that contain syncytotrophoblastic giant cells. [17, 51, 32, 6] Carcinoembryonic antigen (CEA) levels may be increased in nongerminomatous germ cell tumors (NGGCTs) or their components.

Pure germinomas and mature teratomas typically present with normal levels of AFP and beta-hCG in both serum and CSF. Some histologically confirmed germinomas have elevated beta-hCG levels that are presumed to be due to beta-hCG secreting syncytiotrophoblasts. In such cases, elevations of serum beta-hCG are generally limited (<50 IU/L), although some tumors have levels >100 IU/L [14]. (See 'Beta-HCG secreting germinomas' below.)

Any tumor with an elevated AFP (>10 microg/L or higher than the institutional normal range) can be assumed to contain elements of endodermal sinus tumor and/or immature teratoma. If a histologic diagnosis is not possible because surgery is contraindicated, such a patient should be treated as having a NGGCT. Pure endodermal sinus tumor or pure choriocarcinomas are often associated with dramatic elevations in AFP (>500 microg/L) or beta-hCG (>1000 IU/L), whereas immature teratomas have less dramatic elevations of AFP and/or beta-hCG. A serum AFP >1000 microg/L has recently been identified as a poor prognostic indicator [24,25], but since a significant proportion of these tumors have mixed components, it is not yet feasible to use tumor markers for risk stratification without a tissue diagnosis.

References

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