J Pathol Transl Med.  2021 May;55(3):230-234. 10.4132/jptm.2021.03.10.

Hepatoid thymic carcinoma: a case report of a rare subtype of thymic carcinoma

• Jeong JS
• Kang HJ
• Jo U
• Song MJ
• Nam SY
• Song JS

• KMID: 2515928
• DOI: http://doi.org/10.4132/jptm.2021.03.10

Abstract

Hepatoid thymic carcinoma is an extremely rare subtype of primary thymus tumor resembling “pure” hepatoid adenocarcinomas with hepatocyte paraffin 1 (Hep-Par-1) expression. A 53-year-old man presented with voice change and a neck mass. Multiple masses involving the thyroid, cervical and mediastinal lymph nodes, and lung were detected on computed tomography. Papillary thyroid carcinoma was confirmed by biopsy, and the patient underwent neoadjuvant chemoradiation therapy. However, the anterior mediastinal mass was enlarged after the treatment whereas the multiple masses in the thyroid and neck decreased in size. Microscopically, polygonal tumor cells formed solid sheets or trabeculae resembling hepatocytes and infiltrated remnant thymus. The tumor cells showed immunopositivity for cytokeratin 7, cytokeratin 19, and Hep-Par-1 and negativity for α-fetoprotein. Possibilities of germ cell tumor, squamous cell carcinoma, and metastasis of thyroid papillary carcinoma were excluded by immunohistochemistry. This report on the new subtype of thymic carcinoma is the third in English literature thus far.

Keyword

Hepatoid carcinoma; Thymus; α-Fetoprotein; Hep-Par-1

Figure

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  Fig. 1. Radiologic findings. (A) Neck computed tomography (CT) shows a large infiltrating mass with calcification in left thyroid lobe and multiple hypervascular masses in the left level II–VI, left supraclavicular area and right lower neck. (B) The chest CT shows anterior mediastinal mass, measuring 6 cm.

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  Fig. 2. Pathologic findings. (A) Grossly, an ill-demarcated anterior mediastinal mass, measuring 6 cm shows a heterogeneous, tan colored, firm cut surface. (B, C) Microscopically, the polygonal tumor cells formed solid sheet or trabeculae resembling hepatocytes and infiltrated remnant thymus. Part of the tumor shows clear cytoplasm. (D) The tumor cells show distinct cell borders, abundant eosinophilic cytoplasm, and pleomorphic vesicular nuclei.

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  Fig. 3. Representative image of immunohistochemistry. The tumor cells show immune-positivity for cytokeratin 7 (A), cytokeratin 19 (B), and Hep-Par-1 (hepatocyte, C) and negativity for α-fetoprotein (D) by immunohistochemistry

Reference

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