[555] Microcystic Adnexal Carcinoma Versus Desmoplastic Trichoepithelioma: A Histologic and Immunohistochemical Comparison

Julie Y Tse, Long P Le, Anhthu Nguyen, Guilin Wang, Mai P Hoang. Massachusetts General Hospital, Boston, MA

Background: Microcystic adnexal carcinoma (MAC) is a neoplasm with predilection for the head and neck and propensity for local recurrence, necessitating aggressive surgical treatment. Among the differential diagnoses for MAC is desmoplastic trichoepithelioma (dTE), another neoplasm with predilection for the head and neck, albeit with benign biologic behavior. Therefore, accurate diagnostic distinction between MAC and dTE is important in guiding clinical management. However, the histologic distinction between MAC and dTE can be challenging in the setting of a superficial biopsy. In addition, currently only one immunohistochemical stain, carcinoembryonic antigen (CEA), is reported as useful in distinguishing between MAC and dTE.
Design: We reviewed the histologic features of 30 cases of MAC and 39 cases of dTE, and performed CK19 immunostain on 20 MAC and 18 dTE. EGFR immunostain and FISH were done on 18 MAC cases.
Results: MAC cases occurred in older patients in comparison to dTE (median 67 years versus 34 years) and with a 20% recurrent rate. The head and neck was the most commonly involved site, 88% and 89% for MAC and dTE, respectively. In addition to histologic features previously reported as specific for MAC such as skeletal muscle and subcutaneous tissue invasion, perineural invasion, and glandular differentiation, we found the presence of cytologic atypia and mitotic figures to be significantly more frequent in MAC cases by Fisher's Exact test. In contrast, the presence of keratocysts, keratin granulomas and calcification was significantly more frequent in dTE cases (p < 0.0001). CK19 expression was seen in 70% (14/20) and 22% (4/18) of MAC and dTE cases, respectively (p = 0.0044). Strong membranous EGFR expression was noted in all 18 studied MAC cases. However, low polysomy of the EGFR gene was noted in only one MAC case.
Conclusions: The histologic features of keratocysts, keratin granulomas and calcification were significantly more frequent in dTE cases. In addition to features previously reported as specific for MAC, we found the presence of cytologic atypia and mitotic figures to be significantly more frequent in MAC cases. CK19 is a helpful adjunct since it is frequently positive in MAC cases. The role of EGFR inhibitor therapy in MAC cases with protein overexpression remains unclear. The lack of correlation between protein expression and polysomy/gene amplification suggests that molecular mechanisms other than gene amplification play a role in EGFR overexpression in MAC.
Category: Dermatopathology

Tuesday, March 20, 2012 9:30 AM

Poster Session III # 111, Tuesday Morning

 

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