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mediastinal germinoma

Monday 23 January 2012

Primary mediastinal seminoma; mediastinal dysgerminoma

Digital cases

- JRC:258 : Ovarian dysgerminoma.
- JRC:1231 : Mediastinum, anterior: Germinoma with multilocular thymic cyst .
- JRC:19001 : Mediastinum, anterior: thymic germinoma.
- JRC:19005 : Thymic seminoma with marked cystic changes, superior mediastinum.
- JRC:7861 : Mediastinum: Germinoma with yolk sac component.
- JRC:7851 : Mediastinum: Germinoma (embryonal).
- JRC:7852 : Mediastinum: Germinoma.
- JRC:7853 : Mediastinum: Germinoma.
- JRC:7862 : Mediastinum: Germinoma.

Definition: a primitive germ cell tumor, similar to testicular seminoma.

Synopsis

- 90% are apparently unilateral, but occult foci of dysgerminoma can be detected by biopsy of the contralateral ovary in 10% of cases
- monotonous proliferation of primitive germ cells
- connective tissue septa containing variable amounts of chronic inflammatory cells

Immunohistochemistry

- most are vimentin + and PLAP + (placental-like alkaline phosphatase)
- CD117 (c-kit) +
- inconstant + to : cytokeratins, desmin, GFAP, CEA and S-100 protein

Etiology and evolution

- the vast majority have no precursor lesion
- may arise from gonadoblastoma
- may be a precursor to other primitive germ cell tumors

Accurate diagnosis of mediastinal seminoma is critical because of its favorable response to radiation therapy and/or cisplatin-based chemotherapy.

Immunohistochemical staining for OCT4 has recently been validated as a powerful tool for detecting gonadal seminoma.

However, discrepancies between the genetic alterations and immunoprofiles of mediastinal and testicular seminomas have been reported, raising the question of whether techniques that are useful in the diagnosis of gonadal seminoma are applicable to its mediastinal counterpart.

The intense staining pattern of OCT4 and the high sensitivity of FISH make them superior to other auxiliary diagnostic utilities for detecting seminoma.

References

- Primary mediastinal seminoma: a comprehensive assessment integrated with histology, immunohistochemistry, and fluorescence in situ hybridization for chromosome 12p abnormalities in 23 cases. Sung MT, Maclennan GT, Lopez-Beltran A, Zhang S, Montironi R, Cheng L. Am J Surg Pathol. 2008 Jan;32(1):146-55. PMID: 18162782