CME ArticleThe Utility of Myoepithelial Cell Layer Identification in Adnexal CarcinomasPlaza, Jose A. MD*; Chung, Catherine MD†; Wick, Mark MD‡; Sangueza, Martin MD§; Gru, Alejandro MD¶ Author Information *Director of Dermatopathology, Department of Pathology and Dermatology, The Ohio State University Medical Center, Columbus, OH; †Dermatopathologist, Department of Pathology and Dermatology, the Ohio State University Wexner Medical Center, Columbus, OH; ‡Dermatopathologist, Divisions of Dermatopathology, University of Virginia, Charlottesville, VA; §Director of Pathology, Dermatopathology Division, Hospital Obrero, La Paz, Bolivia; and ¶Director of Dermatopathology, Divisions of Dermatopathology and Hematopathology, University of Virginia, Charlottesville, VA. Correspondence: Jose A. Plaza, MD, Director of Dermatopathology, Department of Pathology and Dermatology, The Ohio State University Medical Center, 930 Martha Morehouse Tower, 2050 Kenny Road, Columbus, OH 43221 (e-mail: [email protected]). All authors, faculty, and staff in a position to control the content of this CME activity have disclosed that they have no financial relationships with, or financial interests in, any commercial organizations relevant to this educational activity. The American Journal of Dermatopathology: March 2022 - Volume 44 - Issue 3 - p 155-162 doi: 10.1097/DAD.0000000000001844 Buy CME Test Metrics Abstract The distinction of metastatic carcinomas to the skin (MCS) from cutaneous adnexal carcinomas can pose a significant diagnostic challenge. The differentiation between (MCS) from a primary cutaneous adnexal tumor is one of the most difficult tasks in the field of dermatopathology, and immunohistochemistry has only been partially helpful in solving this problem. In routine diagnostic surgical pathology, it is essential to identify the myoepithelial cell layer by immunohistochemistry to distinguish between an in situ and invasive breast carcinomas and when establishing the presence of microinvasion. The purpose of this study was to evaluate the role of myoepithelial cell layer expression in difficult cases of cutaneous adnexal carcinomas in which histologically it was challenging to separate them from MCS. We studied 38 adnexal carcinomas and evaluated them for myoepithelial markers to confirm the primary nature of the neoplasm. The used markers to search for myoepithelial cell layer retention included calponin, p63, and smooth muscle actin. Of the 38 cases, we found that 13 cases showed myoepithelial layer retention, confirming the primary cutaneous origin of the neoplastic process. The results of our study suggest that the presence of an identifiable retention of the myoepithelial cell layer in adnexal carcinomas could be a useful adjunct observation in the diagnosis of primary adnexal carcinomas, especially in the clinical setting of a questionable primary adnexal versus metastatic neoplasm. Copyright © 2022 Wolters Kluwer Health, Inc. All rights reserved.