Other Frequently Requested Studies

Germ cell tumors are an important category of tumors, as they tend to occur in younger patients, and may have very positive clinical outcomes if appropriate therapy is given. Thus, the pathologist plays an important role in correctly identifying these tumors. For seminoma, placental alkaline phosphatase (PLAP) is a useful positive marker, but is not specific for seminoma, and the use of other markers, such as c-kit, can be helpful. CD30, originally defined with respect to its expression by Reed-Sternberg cells of Hodgkin's lymphoma, has been found to be a positive marker for embryonal carcinoma in this context. Immunohistochemical studies can also reliably identify germ cell tumors in the ovary and testis, discriminating them from other non-germ cell tumors such as granulosa/thecal cell and other stromal tumors of the ovary and Sertoli-Leydig cell, and other non-germ cell tumors of the testis. There are excellent markers of many of these latter tumors, including WT-1, MelanA, and inhibin-alpha.

PLAP A hallmark of testicular seminoma is the strong, uniform expression of placental alkaline phosphatase.	p57 Expression of p57 in cytotrophoblasts, characteristic of partial hydatidiform mole.

Discrimination of complete from partial hydatidiform mole

Because p57^KIP2 is coded by a paternally imprinted gene, antibodies to p57^KIP2 are useful in positively identifying partial hydatidiform mole (positive) from complete hydatiform mole (negative), because complete moles are diploid and derived exclusively from paternal DNA, whereas partial moles are generally triploid and contain maternal and paternal derived genetic material, resulting in normal expression of p57^KIP2.

Cervical dysplasia and p16^INK4a

Expression of p16^INK4a in the cervix is specific for neoplasia and high grade dysplasia, and has been shown to be helpful in improving the accuracy of this diagnosis. p16^INK4a may represent an excellent surrogate marker for the presence of high risk HPV types.

Oncocytic tumors of the kidney

The differential diagnosis of these tumors can include the granular and chromophobe variants of renal cell carcinoma, as well as oncocytoma. In this differential diagnosis, antibodies to E-cadherin, CK7, CK14, and CD10 can be helpful, but the subtleties of the immunostaining patterns, particularly with respect to immunostaining with antibodies to mitochondria, can prove most helpful in this histologic context.

Central nervous system

As outlined in the table below, there are immunohistochemical markers which can positively identify glial tumors, ependymoma, choroid plexus tumors, central neurocytoma, olfactory neuroblastoma, pineal tumors, meningiomas, and medulloblastoma.

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