Mediastinum
Other malignancies
Germ cell tumors

Author: Hanni Gulwani, M.D. (see Authors page)

Revised: 21 June 2018, last major update December 2012

Copyright: (c) 2003-2018, PathologyOutlines.com, Inc.

PubMed Search: Germ cell tumors[TI] mediastinum

Cite this page: Gulwani, H. Germ cell tumors. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/mediastinumgermcell.html. Accessed November 12th, 2018.
Definition / general
  • 20% of mediastinal tumors and cysts
  • Typically divided into seminomas versus nonseminomatous germ cell tumors (teratomas [mature or immature], embryonal carcinomas, yolk sac tumors and choriocarcinoma) (Rev Pneumol Clin 2010;66:63)
  • Malignant transformation of germinal elements without a gonadal focus (Rev Assoc Med Bras 2006;52:182)
Epidemiology
Clinical features
  • Mediastinal tumor in 20 - 49 year old man should be presumed to be a germ cell tumor until proven otherwise
  • Often elevated serum AFP, hCG, HPL, LDH, PLAP
  • Associated with i(12p)+ acute leukemia, Klinefelter syndrome (30x risk)
  • Nonteratomas are often very large at diagnosis
Prognostic factors
  • May have aggressive behavior if not limited to mediastinum at diagnosis (Cancer 1997;80:699, Pediatr Hematol Oncol 2012;29:633)
  • Prognosis worse than gonadal germ cell tumors; 5 year disease free survival is 50 - 65% for seminomas, 20% for other subtypes
  • Sarcomatous component is poor prognostic sign (Am J Surg Pathol 2007;31:1356)
  • Good prognostic factors for nonseminomatous tumors: rapid decline in serum AFP or hCG after surgery and chemotherapy, no vascular invasion, no yolk sac or choriocarcinoma components
Gross description
  • Unencapsulated, homogenous fleshy mass with indistinct boundaries and invasion of adjacent structures, hemorrhage or necrosis
Cytology description
Differential diagnosis
Choriocarcinoma
Epidemiology
  • Usually men in 20s with elevated hCG and gynecomastia, impotence

Prognostic factors
  • Poor prognosis

Case reports
Microscopic (histologic) description
  • Mixed proliferation of syncytiotrophoblasts (large, atypical multinucleated cells with abundant eosinophilic cytoplasm, bizarre nuclei, prominent nucleoli) and cytotrophoblasts (clear cytoplasm, uniform round nuclei, prominent nucleoli, numerous atypical mitoses)

Microscopic (histologic) images

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Resemble Reed-Sternberg cells

CAM5.2+

Diffuse cytotrophoblasts, syncytiotrophoblasts are β hCG+



Cytology images

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Transbronchial aspirate: syncytiotrophoblast



Positive stains
Electron microscopy description
  • Cytoplasmic tonofibrils and plasmalemmal microvilli

Differential diagnosis
  • Metastasis from occult testicular primary: clinical history required
Embryonal carcinoma
Epidemiology
  • Usually males

Gross description
  • Invasive, highly necrotic

Microscopic (histologic) description
  • Poorly differentiated, pleomorphic cells with prominent nucleoli, often with eosinophilic intracellular globules or primitive lumina; variable geographic necrosis
  • No nuclear blebs

Microscopic (histologic) images

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Primitive polygonal cells

Immunostains



Positive stains
Negative stains
Electron microscopy description
  • Well developed junctional complexes, complex nucleoli, primitive microvillous structures or intracellular lumina

Molecular / cytogenetics description
  • i(12p)
Germ cell tumor - mixed
Definition / general
  • Common, describe individual components present and percentage of each

Case reports
Cytology images

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Metastatic tumor

Seminoma
Epidemiology
  • Almost always males

Sites
  • Thymus

Prognostic factors
  • 5 year disease free survival is 50 - 65%; 10 year actuarial survival is 69%
  • Good prognostic factors: age 35 years or less at diagnosis, no superior vena caval syndrome, no mediastinal lymphadenopathy, no fever

Case reports
Treatment
  • Excision, radiation therapy

Gross description
  • Solid, homogenous, tan-white bulging cut surface, residual thymic tissue may be present

Microscopic (histologic) description
  • Nests of large tumor cells with clear cytoplasm (due to glycogen), distinct cell membranes, prominent nucleoli, separated by fibrous stroma with abundant lymphocytes
  • Often epithelioid granulomas, numerous germinal centers, variable geographic necrosis, no nuclear blebs
  • May entrap normal thymus cells

Microscopic (histologic) images

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Thymic seminoma



Positive stains
Negative stains
Electron microscopy description
  • Primitive appositional intercellular junctions, prominent and complex nucleoli (nucleolonemata), abundant cytoplasmic glycogen, no premelanosomes, no complex branching microvilli

Differential diagnosis
Teratoma - immature
Definition / general
  • Teratoma with immature epithelial, mesenchymal or neural elements

Clinical features
Prognostic factors
  • Good prognosis if 14 years old or less

Case reports
Gross images

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Excised tumor with rib



Microscopic (histologic) images

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Primitive glomeruli

Cartilage and ossification

Teratoma - mature
Definition / general
  • Most common mediastinal germ cell neoplasm
  • Benign
  • Peripheral eggshell calcifications in anterior mediastinal mass are relatively specific
  • Often adheres to surrounding structures

Sites
  • May perforate trachea / bronchi, causing patient to cough up hair and oily / sebaceous material

Case reports
Treatment
  • Xanthogranulomatous reaction if sebaceous material escapes

Microscopic (histologic) description
  • Cysts lined by stratified squamous material with sebaceous glands and hair follicles
  • Also cartilage, GI, pancreatic tissue, respiratory structures; may have mature neural tissue

Microscopic (histologic) images

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Postchemotherapy

Various mature tissues

Yolk sac tumor
Definition / general
  • Often mixed with other germ cell elements

Terminology
  • Also called endodermal sinus tumor

Epidemiology
  • Usually males

Prognostic factors
  • Poor prognosis

Case reports
Microscopic (histologic) description
  • Intracellular eosinophilic globules (PAS+, AFP+)
  • Sarcomatoid variant has spindle cells, storiform pattern, myxoid stroma but is otherwise similar

Microscopic (histologic) images

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Various images



Positive stains
Negative stains
Electron microscopy description
  • Redundant basal lamina, globular secretions of AFP+ dense material within rough endoplasmic reticulum