Definition
A germ cell tumour identical to the corresponding gonadal tumour.
Primary mediastinal seminomas accounts for 8% of extragonadal germ cell tumours and 9% to 39% of mediastinal germ cell tumours and 3% to 4% of all mediastinal neoplasms. Mediastinal seminoma is almost exclusively found in males, with most cases occurring the in the third or fourth decade of life.
Presentation is usually secondary to the mass effect. Unlike non-seminomatous tumours, seminomas of the mediastinum are not associated with Klinefelter's syndrome.
Most tumours are circumscribed, without infiltration of adjacent structures. Occasional cases show cystic change, which possibly arises in the residual or hyperplastic thymic tissue2,3.
The morphology is similar to that of gonadal seminomas. They are composed uniform sheet of round or polygonal cells. The cytoplasm contains copious glycogen and often appear clear2. The nuclei show one or more large nucleoli. The cells are usually separated by fibrous septa2. There is often a background of lymphocytes, plasma cells, sometimes eosinophils. There is often granulomatous inflammation2. Occasionally, the inflammation may mask the seminoma. Syncytiotrophoblastic cells are occasionally present, but, in contrast to choriocarcinoma, there is no cytotrophoblastic component.
Seminoma may occur as a component of a mixed germ cell tumour. Spermatocytic seminoma has not been reported in the mediastinum.
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23/232, 11/118 |
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80-90%0, 10/232, 10/114, 40/505, 37/406 |
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70%0 |
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often positive0, 13/232, 3/87 |
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70%0 |
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9/232 |
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3/232 |
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0/232 |
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2/232, 0/114, 0/505 |
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positive in any syncytiotrophoblastic cells0 |
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0/232, 1/406 |
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negative0 |
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negative0 |
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negative0 |
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Mediastinal seminomas differ from testicular seminoma in more often expressing cytokeratins, PLAP and vimentin.
Cytogenetics
Abnormalities, particularly amplifications, of chromosome 12p are common2.
Molecular studies
Primary mediastinal seminoma often shows c-kit mutation, whereas testicular seminoma shows wild type c-kit.
Mediastinal metastases from gonadal primary seminoma is unlikely in the absence of retroperitoneal deposits.
Embryonal carcinoma: cellular pleomorphism is greater, nuclei overlap and cell borders are poorly defined. Fibrous septa and granulomatous inflammation are lacking.
Yolk sac tumour; shows hyaline globules, lack of fibrous septa.
Metastatic melanoma
Lymphoma
Clear cell carcinoma
Mediastinal seminoma is highly responsive to radiotherapy and cisplatin-based chemotherapy. Metastases occur to cervical and abdominal lymph nodes, lung, pleura, chest wall, liver, adrenals, bone and brain. The prognosis is better than for non-seminomatous mediastinal germ cell tumours. The five year survival is 90% with combination chemotherapy.
0 Tumours of the Lung, Pleura, Thymus and Heart. WHO Classification of Tumours. IARC Press 2004.
5 Moran CA, Suster S, Przygodzki RM, et al. Primary germ cell tumors of the mediastinum: II. Mediastinal seminomas--a clinicopathologic and immunohistochemical study of 120 cases. Cancer 1997; 80:691-8 FULL TEXT
This page last revised 18.5.2008.
©SMUHT/PW Bishop