PMC6431456_01
One of the smallest metastatic deposits consists of a few irregularly shaped nests of tumor cells spanning only one millimeter ((a), x100). One of the larger metastatic deposits consists of a fairly well-circumscribed proliferation of tumor cells, which are arranged peripherally in nests and centrally as cords within a sclerotic stroma ((b), x40). The densely sclerotic stroma in this focus of metastatic breast carcinoma resembles the amyloid-type stroma seen in medullary thyroid carcinoma ((c), x100), and the embedded cords and small nests of tumor cells display pronounced retraction artifact ((d), x200). Some metastatic deposits show prominent peripheral rimming of the thyroid follicles by tumor cells, in a pattern reminiscent of C cell hyperplasia ((e), x100). The tumor cells have round nuclei with fine chromatin and prominent nucleoli, ample eosinophilic cytoplasm, and distinct cell borders ((f), x400).
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fig1
Most of the smaller metastatic foci, measuring around 1 millimeter each, consisted of a few irregularly shaped nests of epithelioid tumor cells interspersed between thyroid follicles (Figure 1(a)). The largest metastatic focus measured 0.6 cm and was comprised of tumor cell nests arranged along the periphery of a sclerotic stroma containing cords of tumor cells showing retraction artifact (Figures 1(b)-1(d)). Additionally, there were numerous areas of rimming of the thyroid follicles by the tumor cells, which mimicked the appearance of C cell hyperplasia (CCH) (Figure 1(e)). Where arranged as nests, cell borders were distinct between the tumor cells, which contained centrally placed monomorphic round nuclei, finely granular chromatin, prominent nucleoli, and a moderate amount of eosinophilic cytoplasm (Figure 1(f)).
The tumor cells express nuclear positivity for ER ((a), x200) and GATA3 ((b), x200) immunohistochemistry, and diffuse membranous staining with e-cadherin ((c), x200).
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Immunohistochemical stains showed that the tumor cells were positive for cytokeratin AE1/AE3, ER, GATA3, and e-cadherin (Figure 2), while they were negative for CK7, CK20, GCDFP/mammaglobin, TTF-1, thyroglobulin, calcitonin, and synaptophysin.