[507] Clinicopathologic Features of Cutaneous Syncytial Myoepithelioma

Vickie Y Jo, Jason L Hornick, Christopher DM Fletcher. Brigham and Women's Hospital & Harvard Medical School, Boston, MA

Background: Cutaneous myoepithelial tumors demonstrate heterogeneous morphologic and immunophenotypic features. We previously described a subset of cutaneous myoepitheliomas showing solid syncytial growth of ovoid, spindled or histiocytoid cells. We now present the clinicopathologic features of 36 cases of the distinctive syncytial variant of cutaneous myoepithelioma.
Design: 36 cases identified between 1997 and 2011 were retrieved from surgical and consultation files. 6 cases have been published previously. H&E and immunohistochemical stains were examined. Clinical and follow-up information was obtained from referring pathologists.
Results: Patients were 25 men and 11 women, with a median age of 36 years (range 2 months to 74 years). Anatomic sites were upper extremity (11), upper limb girdle (3), lower extremity (13), back (5), face (2), chest (1), and buttock (1). Lesions ranged in size from 0.3 to 2.7 cm (median 0.7 cm) and were well circumscribed and either polypoid or papular. All tumors were centered in the dermis. Microscopically all tumors showed a solid sheet-like growth of uniformly sized ovoid to spindled or histiocytoid cells with pale eosinophilic syncytial cytoplasm. Nuclei were vesicular with fine chromatin and small or inconspicuous nucleoli, and showed mild to no atypia. Mitoses ranged from 0 to 4 per 10 HPF; 26 tumors showed no mitoses. All tumors lacked necrosis and lymphovascular invasion. Adipocytic metaplasia, appearing as superficial fat entrapped within the tumor, was seen in 9 cases. Chondro-osseous differentiation was seen in 1 tumor. All tumors examined were diffusely positive for EMA and S-100 protein. Keratin staining was focal in 1 of 33 tumors and seen in rare cells in 2 other cases. There was also positivity for GFAP (14/31), SMA (9/13), and p63 (6/11). Most patients were treated by local excision. Follow-up information is available for 19 patients so far (mean follow-up 16 months); all are alive with no evidence of disease, including 7 patients who had positive deep margins. None has recurred to date.
Conclusions: Cutaneous syncytial myoepithelioma is a distinct variant that more frequently affects men, occurs over a wide age range, and usually presents on the extremities. Tumors are positive for S-100 and EMA, and unlike most myoepithelial neoplasms, keratin staining is infrequent. Prior reports describe some risk of recurrence and metastasis for cutaneous myoepithelial tumors; however, based on preliminary follow-up data, the syncytial variant appears to behave in a benign fashion.
Category: Dermatopathology

Tuesday, March 20, 2012 9:30 AM

Poster Session III # 121, Tuesday Morning


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