Cutaneous syncytial myoepithelioma: A recently described neoplasm which may mimic nevoid melanoma and epithelioid sarcoma

Abstract

Cutaneous syncytial myoepithelioma is a recently described rare tumor of the dermis. It is derived and composed purely of myoepithelial cells and shows a characteristic syncytial growth pattern of neoplastic cells with little intervening stroma and no recognizable ductal structures. It represents a diagnostic challenge to dermatopathologists given its rarity and unusual immunophenotype. Molecular testing for rearrangement of the EWSR1 gene plays a significant role in confirming the diagnosis in most cases. Herein, we present 2 cases with mundane clinical presentations and challenging histopathological findings. In both cases, the lesion was composed of relatively well‐circumscribed proliferation of epithelioid and spindle cells in the superficial dermis growing in a syncytial fashion and showing focal adipocytic metaplasia. The 2 cases had slightly different immunohistochemical profiles, but shared focal positivity for S100, EMA and pan‐keratin or p63. Break‐apart FISH demonstrated the presence of an EWSR1 gene rearrangement confirming the diagnosis in both cases. We discuss the most important differential diagnoses, particularly melanocytic lesions and epithelioid sarcoma and the original diagnostic considerations that the cases were referred to us with. We also review the molecular features and spectrum of immunohistochemical findings in these lesions and their role in excluding entities in the differential diagnosis.

Cutaneous syncytial myoepithelioma: A potential pitfall in the differential diagnosis of superfi cial dermal tumors

“…These tumors are negative for CK by immunohistochemistry unlike CM and have distinctive molecular characteristics [8]. These tumors are benign such as CM and rarely recur when incompletely resected [7,8] In the current study, we also reported a CSM case with dermis-located and well-cirumscribed tumor displays a showed pseudoepitheliomatous hyperplasia (Figure 1 Immunohistochemically, cellular neurothekoma exhibits no positivity for EMA or S100 [11]. [15].…”

EWSR1‐PBX3 gene fusion in cutaneous syncytial myoepithelioma

“…Of interest, reports describing and illustrating this type of ME neoplasm in the skin were published in the literature of dermatopathology long before the coining of the term “cutaneous syncytial myoepithelioma.” Histopathologically, the lesion forms an unencapsulated dermal nodule, similar to that seen in other cutaneous myoepitheliomas, and like those tumors it exhibits a range of cytological appearances including spindled, ovoid, and/or epithelioid cells with pale eosinophilic cytoplasm and monomorphous nuclei displaying fine chromatin and small nucleoli . The syncytial arrangement of the cells is characteristic, with little or no intervening stroma and absence of ductal or glandular structures . Mitotic activity is infrequent, and when present does not alter the diagnosis or prognosis .…”

“…The true incidence of CSM, a recently recognized variant of cutaneous ME tumors, is unknown . To date, it has occurred predominantly in men, across a broad age range.…”

“…Because CSM often generates a diagnostic quandary in a clinical setting, additional information about its genetic characteristics would be valuable. This is exemplified by the fact that nevoid melanoma and epithelioid sarcoma enter the differential diagnosis . Further investigation of the range of EWSR1 pairings in these lesions will likely prove to be not only of academic but also of practical value.…”

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

“…The syncytial variant of cutaneous myoepithelioma is a reproducible cutaneous subtype with a dome-shaped silhouette and sheets or syncytia of epithelioid, plasmacytoid, and/or spindled cells with ovoid monomorphous nuclei. 7,8,11,12 The immunophenotype is often variable, sometimes overtly inconsistent with conventional myoepithelioma, which produces pitfalls in diagnosis. Immunopositivity with S100, EMA, and SMA are most frequent.…”