Cutaneous Syncytial Myoepithelioma: A Nondescript Skin Tumor With Serious Diagnostic Pitfalls

Abstract

Cutaneous syncytial myoepithelioma (CSM) is a rare tumor with a nondescript clinical presentation in the skin. It represents a relatively uncommon diagnostic entity with approximately 50 examples in the literature to date. We present a 36-year-old man with a new, tender 3-mm firm pink papule on the left bicep, in which a superficial shave technique produced a diagnostic challenge. CSM often poses a diagnostic quandary given shared histomorphological and immunohistochemical attributes with superficial mesenchymal or neurocristic tumors, namely, melanocytic proliferations, fibrous histiocytoma, and epithelioid sarcoma. The molecular profile of CSM may reveal EWSR1 or FUS gene rearrangement, but as we showcase, the diagnosis remains possible in the absence of this oncogenic fusion. Ultimately, there are pitfalls to avoid to correctly distinguish this benign myoepithelial lesion from more biologically aggressive neoplasia.

Cutaneous syncytial myoepithelioma with folliculocentric growth and EWSR1 gene rearrangement: A case report

“…There are a few reports of CSM cases diagnosed by immunohistochemistry without fusion gene investigation 13,14 . However, several case reports have described the diagnostic challenge in making a diagnosis of CSM by immunohistochemistry alone.…”

“…12 There are a few reports of CSM cases diagnosed by immunohistochemistry without fusion gene investigation. 13,14 However, several case reports have described the diagnostic challenge in making a diagnosis of CSM by immunohistochemistry alone. One case report demonstrated a lesion with atypical immunohistochemical results mimicking nevoid melanoma or epithelioid sarcoma that was eventually diagnosed as CSM with an EWSR1 rearrangement on break-apart FISH.…”

Cutaneous Syncytial Myoepithelioma: A Unique Variant Worth Recognizing

“…If a pathologist is not familiar with the CSM morphology, it can pose a potential diagnostic pitfall [ 21 ]. Careful inspection of microscopic features and a panel of immunohistochemical stains can aid in establishing the correct diagnosis and rule out clinically significant entities in the differential.…”

Recent Advances on Immunohistochemistry and Molecular Biology for the Diagnosis of Adnexal Sweat Gland Tumors

“…EWSR1::PBX3 fusions are more frequent in syncytial myoepithelioma compared to other cutaneous myoepitheliomas [80][81][82]. In extracutaneous myoepitheliomas, EWSR1::POU5F1 and EWSR1::PBX3 are the two most frequent fusions [76], while FUS::KLF17, EWSR1::PBX1, EWSR1::ZNF444, EWSR1::KLF15, FUS::POU5F1, EWSR1::KLF17, EWSR1::FUS, EWSR1::ATF1, and EWSR1::VGLL1 are less frequent [60,76,[83][84][85][86][87][88]. POU5F1-rearranged myoepitheliomas show a distinctive clear cell appearance that can be mistaken for hidradenoma, and PBX1-rearranged myoepitheliomas show sclerosis [60].…”