Immunohistochemical Biomarkers of Mesenchymal Neoplasms in Endocrine Organs: Diagnostic Pitfalls and Recent Discoveries.

Mesenchymal neoplasms rarely present in or adjacent to endocrine organs. In this context, the recognition of these rare tumor types can be challenging, with significant potential for misdiagnosis as sarcomatoid carcinomas (i.e., anaplastic thyroid carcinoma and sarcomatoid adrenal cortical carcinoma) or neuroendocrine carcinomas, depending upon the dominant histologic patterns. In this review, we address potential pitfalls in diagnosing selected mesenchymal neoplasms arising within or near endocrine organs, including dedifferentiated liposarcoma, synovial sarcoma, angiosarcoma, PEComa, proximal-type epithelioid sarcoma, Ewing sarcoma, and neuroblastoma. For each of these tumor types, we review clinical and pathologic features, histologic clues to distinguish them from endocrine neoplasms, and recently developed immunohistochemical markers that can be particularly useful for establishing the correct diagnosis.