Answer and Discussion of Quiz Set: N-001

4.    Which of the following is not true about immunohistochemistry for OCT-4?

A.  OCT-4 is a transcription factor in embryonic stem cells and germ cells that maintains and regulates pluripotency of these cells.

B.  Its genuine positive immunoreactivity is cytoplasmic labeling.

C.  It is positive in seminoma and embryonal cell carcinoma but negative in yolk sac tumor and choriocarcinoma.

D.  Seminoma cells in tumors with heavy inflammatory cell infiltration can be detected by immunohistochemistry for OCT-4, placental alkaline phosphatase (PLAP) and CD117 (c-kit).

Answer and Discussion: The answer is (B). The genuine positive immunoreactivity is nuclear for OCT-4. In general, genuine positive immunoreactivity for transcription factor (such as thyroid transcription factor-1 or TTF-1) are in the nucleus. OCT-4 is a transcription factor in embryonic stem cells and germ cells that maintains and regulates pluripotency of these cells. It is positive in seminoma and embryonal cell carcinoma but negative in yolk sac tumor and choriocarcinoma. Serminomatous tumor, including germinoma of the pineal gland, can be accompanied by an intense lymphocytic infiltration. They may also undergo extensive granulomatous changes. Both situations makes identification of the tumor cell a difficult hunting task and both would also suggest infection. In the case of pineal germinom, a tumor in the pineal region in a young adult or child with no clinical sign of infection is a strong suggest of neoplasm rather than infection. This is a helpful hint for correct diagnosis. OCT-4, PLAP, and CD117 can all be used to identify the seminomatous cells. It should note that CD117 is very sensitive for this purpose but not as specific as OCT-4 or PLAP.