Mediastinal embryonal carcinoma

Last revised by Dr Joachim Feger on 27 Dec 2021

Mediastinal embryonal carcinomas or embryonal carcinomas of the mediastinum are malignant non-seminomatous germ cell tumors with embryonal type cells primarily growing in the mediastinum.

Mediastinal embryonal carcinomas are very rare mediastinal tumors accounting for up to 8% of primary mediastinal germ cell tumors 1. They usually occur in young men up to the fourth decade and less often in boys.

Klinefelter syndrome is a considered risk factor 1,2.

The final diagnosis is based on histology, gender and age as well as immunohistochemistry 1.

Diagnostic criteria according to the WHO classification 1:

  • large polygonal cells with an indistinct tumor cell membrane, amphophilic or eosinophilic cytoplasm and single or multiple large nucleoli
  • solid, papillary glandular/tubular growth

Further desirable criteria are the following 1:

  • young male gender
  • expression of SALL4, OCT4, SOX2, CD30 and cytokeratins
  • negativity for KIT/CD117 and CD45

A large heterogeneous mediastinal mass with lung metastases in young men in the setting of rapid symptom onset and an elevated LDH and serum AFP might point to a malignant non-seminomatous germ cell tumor.

Clinical signs and symptoms are frequently related to the mediastinal mass and include dyspnea, chest pain, cough and hemoptysis as well as superior vena cava syndrome. Systemic symptoms include weight loss, fever and chills 1,2. Serum LDH might be elevated. Elevated serum AFP levels have been reported but this suggests yolk sac tumor elements 1,2.

Mediastinal embryonal carcinomas might cause the following complications 1-3:

Mediastinal embryonal carcinomas are malignant non-seminomatous germ cell tumors characterized by embryonal cells 1.

Assumptions include the origin from local embryonic stem cells and an aberrant midline migration of primordial germ cells 1.

Mediastinal embryonal carcinomas are usually located in the anterior mediastinum 1.

Mediastinal embryonal carcinomas are often large at the time of diagnosis. Tumor sizes of >20 cm have been reported. The cut surface might show areas of necrosis and/or hemorrhage 1.

Histologically mediastinal embryonal carcinomas display the following features 1,2:

  • large and pleomorphic cells
  • eosinophilic or amphophilic cytoplasm
  • indistinct cell membranes
  • large single or multiple nucleoli
  • many and atypical mitoses
  • solid sheets, tubular/glandular or papillary growth patterns
  • variable geographic necrosis
  • variably syncytiotrophoblasts

Immunohistochemistry stains of mediastinal embryonal carcinomas express OCT4, SALL4, CD30, SOX2 and cytokeratins. β-hCG is positive in a minority of cases. KIT/CD117 is usually negative 1.

Imaging features of mediastinal embryonal carcinomas are unspecific and heterogeneous. Tumors might get quite large and displace or infiltrate the adjacent mediastinal structures and/or vessels 2-4.

Chest x-ray might show widening of the anterior mediastinum with silhouette sign or a broadening of the anterior junction line 3,4.

On chest CT mediastinal embryonal carcinomas have been described as lobulated, poorly marginated and heterogeneous masses, areas of necrosis and hemorrhage are common 3-4. Pleural or pericardial effusions might be present.

PET-CT displays high uptake of FDG and might be used to monitor therapy.

The radiological report should include a description of the following:

  • location and extent of the tumor
  • relation to the heart and great vessels
  • associated complications (e.g. superior vena cava obstruction, pleural or pericardial effusion)
  • nodal disease
  • distant metastases

Therapy is not different from other malignant non-seminomatous germ cell tumors and includes chemotherapy with subsequent surgery. Mediastinal embryonal carcinomas metastasize to lung and/or lymph nodes and the prognosis is poor 1.

Condition or tumors that might mimic the appearance of mediastinal embryonal carcinomas include 1:

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