PMC6077660_01
Background follicular adenoma: Microfollicles with scant colloid lined by cells with bland round to oval nuclei.
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fig1
The tumour showed predominantly areas in keeping with usual follicular adenoma formed by microfollicles with scant colloid and lined by cells with bland round to ovoid nuclei (Figure 1).
PDTC-like region with insular pattern and altered nuclear morphology.
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fig2
The mitotic count was very high (8/10 high power fields), although tumour necrosis was absent, meeting criteria for PDTC (Figure 2).
(A) Low power view of PDTC-like focus and adjacent trabecular region that does not fulfil PDTC criteria; (B) PDTC-like focus and adjacent trabecular region showing higher MIB-1 proliferation index; (C) all areas showing retained of TTF1; (D) PDTC-like focus showing loss of thyroglobulin expression and trabecular region with reduced expression.
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fig3
In addition there were several regions, one of which was adjacent to the PDTC-like area, showing formation of trabeculae and high nuclear cytoplasmic ratio, without sufficient nuclear morphology or mitotic count for PDTC criteria (Figure 3(a)). The PDTC-like focus and adjacent trabeculae region did show noticeably higher proliferation rate by MIB1 immunohistochemical (IHC) staining (Figure 3(b)). TTF1 (Figure 3(c)), with loss of thyroglobulin (which was retained in background follicular adenoma component and reduced expression in the adjacent trabeculae area) (Figure 3(d)). There was no expression of calcitonin, synaptophysin, chromogranin, or BRAFVE1 IHC staining.