Mediastinum
Thymic carcinoma
Lymphoepithelioma-like thymic carcinoma


Topic Completed: 7 May 2019

Revised: 7 May 2019

Copyright: 2003-2019, PathologyOutlines.com, Inc.

PubMed Search: Lymphoepithelioma-like thymic carcinoma
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Cite this page: Suster D, Mackinnon AC. Lymphoepithelioma-like thymic carcinoma. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/mediastinumLEL.html. Accessed May 22nd, 2019.
Definition / general
  • Also known as poorly differentiated, nonkeratinizing, squamous cell thymic carcinoma
  • Originates from thymic epithelial cells and shows histologic and immunophenotypic evidence of squamous differentiation
  • WHO classification: lymphoepithelioma-like carcinoma
Essential features
  • Defined as a primary thymic epithelial neoplasm displaying overt cytologic evidence of malignancy with loss of organotypical features of thymic differentiation
  • Diagnosis of exclusion
  • Invasive growth pattern of nests and cords of tumor cells which grow in a syncytial growth pattern and have vesicular nuclei with prominent nucleoli
  • Often have prominent associated lymphoid infiltrate within fibrous stroma
  • Rare cases associated with Epstein-Barr virus (EBV)
Terminology
  • Thymic carcinoma
  • Poorly differentiated, nonkeratinizing, squamous cell thymic carcinoma
  • Lymphoepithelioma-like carcinoma
ICD coding
  • ICD-10: C37 - thymic carcinoma (malignant)
Epidemiology
  • M > F (~3:1)
  • Average age of 60 years (range: 20 - 85 years)
Sites
Etiology
  • Remains unknown
  • Epstein-Barr virus has been reported in rare case reports, predominantly in younger patients; however, in the largest study, only 4% of cases were positive for EBER by in situ hybridization (Am J Surg Pathol 2018;42:1224)
  • No pathognomonic molecular alterations have been identified
Clinical features
  • Present with anterior mediastinal masses, often found incidentally
  • When symptomatic, clinical symptoms include chest pain, shortness of breath and weight loss (Am J Surg Pathol 2018;42:1224)
Radiology description
  • Typically appear as well demarcated anterior mediastinal masses
  • Positron emission tomography (PET) usually shows mild to moderate PET avidity
Prognostic factors
Case reports
Treatment
  • Surgical resection is still the predominant treatment
  • Radiotherapy may increase local regional relapse free survival with mild toxicities in advanced stage patients (Ann Thorac Surg 2017;104:1718)
  • In the largest study, 14 of 20 patients had no evidence of disease between 1.5 and 16 years after diagnosis (median survival: 4 years; mean survival: 5.5 years) (Oncol Lett 2014;8:2183)
Microscopic (histologic) description
  • Invasive growth pattern of cords, nests and trabeculae separated by fibrous stroma with variable prominent mature lymphoid infiltrates
  • 2 patterns of growth described (Am J Surg Pathol 2018;42:1224):
    • Lymphoepithelioma-like pattern: irregular cords and islands of tumor cells separated by connective tissue stroma containing dense lymphoplasmacytic infiltrates
    • Desmoplastic pattern: irregular cords and nests of tumor cells separated by fibrous stroma with minimal inflammatory infiltrates
    • Can have both patterns
  • Can show focal areas of abrupt keratinization
  • Prominent areas of comedonecrosis
  • Uniform, poorly differentiated tumor cell population with round to oval nuclei, vesicular chromatin, prominent round eosinophilic nucleoli and an indistinct rim of eosinophilic cytoplasm
  • Syncytial growth pattern of tumor cells with rare pleomorphic and multinucleated cells
Microscopic (histologic) images

Contributed by David Suster, M.D.

Sheets of large round to oval tumor cells

Anastomosing cords, islands, comedonecrosis

Comedonecrosis

Lymphoepithelioma-like pattern


Desmoplastic pattern

Focal abrupt keratinization

p63

Electron microscopy description
  • Cohesive population of large cells with round to oval nuclei containing a single nucleolus and scattered heterochromatin (Am J Surg Pathol 2018;42:1224)
  • Abundant junctional complexes, with dense plaques and well formed desmosomes containing attached short tonofilaments (Am J Surg Pathol 2018;42:1224)
Electron microscopy images

Contributed by David Suster, M.D.

Large, round tumor cell

2 desmosomal attachments

Molecular / cytogenetics description
Sample pathology report
  • Thymus, resection:
    • Poorly differentiated thymic squamous cell carcinoma, predominantly nonkeratinizing (lymphoepithelioma-like) (see synoptic report and comment)
    • Comment: The tumor cells are positive for p40, CD117, CD5 and PDL1.
Differential diagnosis
Board review question #1
A 62 year old patient presents with a 9 cm anterior mediastinal mass (see image below). What specific test would help differentiate this lesion from a metastasis from a head and neck lymphoepithelioma-like thymic carcinoma?



  1. Immunohistochemistry for p63 and cytokeratins
  2. In situ hybridization for EBER
  3. In situ hybridization for HPV
  4. Next generation sequencing
Board review answer #1
B. In an older patient, in situ hybridization for EBER would be the most helpful test as nearly 100% of head and neck lymphoepithelial carcinomas are EBER+ while thymic lymphoepithelial carcinomas tend to be EBER-, especially in adults.

Reference: Lymphoepithelioma-like thymic carcinoma

Comment Here
Board review question #2
Which immunohistochemical stains would be most helpful in distinguishing a primary squamous cell thymic carcinoma from metastatic lesions from other primary sites?

  1. CD5 and CD117
  2. Cytokeratins
  3. p16
  4. p63
Board review answer #2
A. CD5 and CD117 would be the most helpful in establishing thymic origin in this scenario. While primary lymphoepithelioma-like thymic carcinoma will express keratins, p16 and p63, so would poorly differentiated squamous cell carcinomas elsewhere in the body. However, few lesions outside the body would have CD5 and CD117 positivity.

Reference: Lymphoepithelioma-like thymic carcinoma

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