FIGURE 3: A , H&E image of EHE with plump neoplastic atypical vascular endothelial cells (inset 1, arrow) compared to admixed normal benign flattened and spindle endothelial cells (inset 2, star).B. CD31 immunostain highlighting membranes of neoplastic cells. C, FLI-1 immunostain highlighting large irregular nuclei of neoplastic cells. A horseradish peroxidase-diaminobenzidine (HRPO-DAB) detection system was used. Original magnification of A-C (400x).
A wide panel of antibodies was employed to further characterise this lesion. CD34, CD31 and FLI-1 immunopositivity confirmed vascular endothelial origin. Metastatic carcinoma was ruled out by negative staining for AE1/AE3 and Cam5.2 (cytokeratins). In light of thyroid nodule, additional TTF-1 and PAX8 stains were employed to rule out metastatic PTC; these were both negative. They are crucial for thyroid organogenesis and differentiation and are thus invariably positive in the presence of thyroid metastasis9. Less likely entities such as epithelioid sarcoma and haemangioblastoma were excluded by negative immunostaining results for INI-1 and inhibin, respectively.
As the lesion showed well-formed vessels as opposed to the more classic blister cells and myxohyaline stroma, a TFE3 antibody was employed to assess for the presence of a YAP1-TFE3 gene fusion which is characteristic in this subset of EHE. The TFE3 results were, unfortunately negative.
There is no locally available FISH platform to assess the presence of the WWTR1-CAMTA1 gene fusion nor is there a locally available fusion specific antibody.
Overall the architectural, cytomorphological atypia and immunohistochemical features are that of an atypical vascular lesion. The features are more atypical than that haemangioma but fall short of the significant atypia of angiosarcoma. Therefore a consensus diagnosis of EHE was reached.