Intrathyroidal thymic carcinoma comprising squamous cell and small cell carcinoma components: A case report

Figure 1 The histomorphology of the tumour reveals two distinct components: Squamous cell carcinoma and small cell carcinoma. In the squamous cell carcinoma region: At 100 × magnification, abundant stroma components are visible, with nest of tumour cells forming islands separated by the stroma; at 200 × magnification, the tumour cells exhibit slightly eosinophilic cytoplasm, pale vacuolated nuclei, and prominent nucleoli. In the small cell carcinoma region: At 100 × magnification, the tumour cells are arranged in sheets, with minimal surrounding stroma; at 200 × magnification, the tumour cells display scanty cytoplasm, poorly defined cell borders, finely granular and lightly stained chromatin, and inconspicuous nucleoli. Scale bar is 60 μm. SCC: Squamous cell carcinoma; SmCC: Small cell carcinoma.

Figure 2 Immunochemical analysis revealed two distinct tumour components: Squamous cell carcinoma and small cell carcinoma. The squamous cell carcinoma component demonstrated positive staining for cluster of differentiation (CD) 5, CD117, cytokeratin and p40, with a Ki-67 proliferation index of 30%. The small cell carcinoma component showed positivity for CD117, cytokeratin, synaptophysin and chromogranin A, exhibiting a higher Ki-67 proliferation index of 60%. Scale bars are 60 μm. At 200 × magnification. SCC: Squamous cell carcinoma; SmCC: Small cell carcinoma; CD: Cluster of differentiation; TdT: Deoxynucleotidyl transferase; CK: Cytokeratin; Syn: Synaptophysin; CgA: Chromogranin A.

Figure 3 The transitional zone between the two tumor components. Hematoxylin and eosin staining revealed a gradual morphological transition from nests of squamous cell carcinoma to sheets of small cell carcinoma. A corresponding change was observed in the immunohistochemical staining patterns of synaptophysin and chromogranin A across this region. Scale bars are 600 μm. At 20 × magnification. HE: Hematoxylin and eosin; Syn: Synaptophysin; CgA: Chromogranin A.

Figure 4 Imaging examinations. A: Thyroid ultrasonography showing a mass with regular morphology and well-defined margins, closely associated with the lower pole of the thyroid gland; B: Contrast-enhanced axial computed tomography scan of the neck demonstrating a large mass causing tracheal deviation. The orange dotted line outlines the approximate tumor extent, and the green arrow indicates the deviated trachea.