Original StudyDifferentiation of Basal Cell Carcinoma and Trichoepithelioma: An Immunohistochemical StudyCarrasquillo, Osward Y. MD, MPH*; Cruzval-O'Reilly, Estefanía BA†; Sánchez, Julio E. MD*; Valentín-Nogueras, Sheila M. MD*Author Information *Department of Dermatology, University of Puerto Rico School of Medicine, San Juan, PR; and †Universidad Central del Caribe School of Medicine, Bayamon, PR. Correspondence: Osward Y. Carrasquillo, MD, MPH, Department of Dermatology, University of Puerto Rico School of Medicine, PO Box 365067, San Juan, PR 00936-5067 (e-mail: [email protected]). The authors declare no conflicts of interest. The American Journal of Dermatopathology: March 2021 - Volume 43 - Issue 3 - p 191-197 doi: 10.1097/DAD.0000000000001783 Buy Metrics Abstract Basal cell carcinoma (BCC) is the most common malignancy of the skin. It is an epithelial neoplasm with origin in the precursor cells of the interfollicular epidermis. Even though it has low metastatic potential, delay in management may lead to local destruction and morbidity. In contrast, trichoepithelioma (TE) is a benign tumor originating from the outer root sheath of the hair follicle. Similar to BCC, TE tends to affect the head and neck region. Both neoplasms may exhibit clinical and histopathological similarities, making them prone to misdiagnosis. Multiple immunomarkers have been used to distinguish among these entities, but so far, no single agent or combination of agents appear to be neither sensitive nor specific enough to differentiate between them. This study was divided into 2 parts. First, 17 cases of BCC and 14 cases of TE were stained with androgen receptor and bcl-2. Then, 27 cases of borderline/equivocal of BCC and 13 cases of borderline/equivocal TE were stained with the same protocol. Sensitivity and specificity were calculated for each individual immunomarker and for the combination of them. Androgen receptor positivity was 100% specific for BCC and borderline/equivocal BCC, whereas bcl-2 diffuse staining pattern demonstrated a sensitivity of 82.4% for BCC and 88.9% borderline/equivocal BCC. When both immunomarkers were combined, the sensitivity for BCC decreased (70.6%) but the specificity remained high (100%). Similarly, the sensitivity for borderline/equivocal BCC was 55.6%, whereas the specificity was 100%. Although moderately sensitive, combining both immunomarkers showed an excellent specificity to discriminate between BCC and TE. Copyright © 2020 Wolters Kluwer Health, Inc. All rights reserved.