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

In the spectrum of myoepithelial tumors of the skin, cutaneous myoepithelioma is composed solely of myoepithelial cells. Cutaneous syncytial myoepithelioma as a rare histological variant of cutaneous myoepithelioma has been fi rst described in the last decade. This tumor is benign and rarely shows recurrence when incompletely resected. In addition to its distinctive common histological and immunohistochemical features, cutaneous syncytial myoepithelioma shares the same changes for most cases in molecular testing (EWS RNA binding protein 1 gene rearrangement). The differential diagnosis of other superfi cial dermal tumors is one of the major diffi culties in the diagnosis of this tumor. In the current study, we present our fi ndings of a 56 year-old woman who was diagnosed as cutaneous syncytial myoepithelioma. Case Report Cutaneous syncytial myoepithelioma: A potential pitfall in the differential diagnosis of superfi cial dermal tumors Erdem Comut* and Nese Calli Demirkan Faculty of Medicine, Department of Pathology, Pamukkale University, 20160, Denizli, Turkey Received: 24 August, 2019 Accepted: 12 September, 2019 Published: 13 September, 2019 *Corresponding author: Erdem Comut, Faculty of Medicine, Department of Pathology, Pamukkale University, 20160, Denizli, Turkey, Tel: +90-258-29660-00; GSM: +90-506-605-39-56; E-mail:

CM generally affects male adults (with peak incidence in the 3. and 5. decades, and a male to female ratio of 3:1) and extremities as anatomical localization [1,[6][7][8]. It is composed solely of myoepithelial cells and regarded as a subgroup of cutaneous mixed tumor. These tumors usually present as a solitary, slow growing papule and histologically demonstrate a wide spectrum of features including epithelioid, spindled, histiocytoid or plasmocytoid cells showing solid, lobulated or reticular growth patterns in a myxoid or hyalinized stroma [7,9]. Immunohistochemically, neoplastic cells express EMA (epithelial membrane antigen) and S100 protein. Other markers like cytokeratins (CK), GFAP, SMA and p63 show variable expression [6,7,9]. As a rare histologic variant, CSM has been lately described and to the best of our knowledge, there are only 42 cases reported in the literature [8]. This variant demonstrates tightly packed histiocytoid-spindle cells growing in a sheet like pattern within a limited stroma. 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]. At this point, we present our fi ndings of a 56 year-old woman represented clinically by a papule on her left thigh and diagnosed as CSM in our department.

Results
The lesion was described as a solitary, well-circumscribed,     Immunohistochemically, both neoplasms are EMA (+), on the other hand, EBFH lacks reactivity for myoepithelial markers including S100 [8,10].
Juvenile xantogranuloma (JXG) is a neoplasm that usually affects infants and young children. This neoplasm is composed of histiocytic cells and lacks the characteristic multinucleated giant cells especially in the early-stage lesions, so it should be considered in the differential diagnosis of CSM. JXG is negative for EMA and S100 protein, but shows CD68 and CD163 positivity [10,12].
As a histologic variant of neurothekoma, cellular neurothekoma may also mimic CSM due to the composition of this tumor with spindled and epithelioid cells with abundant eosinophilic cytoplasm and indistinctive cell borders.
Immunohistochemically, cellular neurothekoma exhibits no positivity for EMA or S100 [11]. EWSR1 gene is located on the long arm of chromosome 22 at position 12.2 [13]. Although its function is not fully understood, EWSR1 protein takes part in cellular processes, cell signaling and RNA transport [14]. Mutations of EWSR1 gene are seen in a wide range of tumors including Ewing sarcoma, desmoplastic small round cell tumor, extraskeletal myxoid chondrosarcoma, clear cell sarcoma of soft tissue, myxoid liposarcoma and soft tissue myoepithelial tumors [15]. Rearrangement of this gene has been detected nearly half of CM cases [16]. Fletcher reported EWSR1 gene rearrangement was found in most CSM cases. Pre-B-Cell Leukemia Homeobox 3 (PBX3) has been determined as a fusion partner of EWSR1 in one study [17].
In conclusion, CSM is a lately described entity and represents a diagnostic challenge in terms of superfi cial dermal tumors.
Because of its rarity and diagnostic diffi culties, most CSM cases are referred to experienced pathologists with various initial diagnoses. Since EWSR1 gene rearrangement is seen in most cases, molecular testing can help to confi rm the diagnosis of this tumor in addition to some prominent histopathological and immunohistochemical features. CSM rarely shows local recurrence when incompletely resected, otherwise it presents as a benign tumor.