Extraordinary Case ReportClear Cell Hidradenoma—Basal Cell Carcinoma CollisionPiqué-Duran, Enric MD*; Duran-Hernández, MªCristina MD†; Pérez-Cejudo, Juan A. MD*; García-Vázquez, Odalys MD† Author Information Departments of *Dermatology, and †Department of Pathology, Dr José Molina Orosa Hospital of Lanzarote, Arrecife, Spain. Correspondence: Enric Piqué-Duran, MD, Dermatology Department, Ctra Arrecife-Tinajo, km 1,3, Arrecife de Lanzarote 35500, Spain (e-mail: [email protected]). The authors declare no conflicts of interest. The American Journal of Dermatopathology 43(2):p e23-e26, February 2021. | DOI: 10.1097/DAD.0000000000001763 Buy Metrics Abstract A 91-year-old man presented with a tumor on the left temporal area, clinically suspicious of basal cell carcinoma. The histopathologic study showed a central solid-cystic tumor composed by 3 different types of cells (clear or finely granular cells, polygonal cells, and squamoid cells). It had a sclerotic stroma. At the periphery, another tumor composed by smaller interconnected nests was evident. Some nests were separated from the stroma by clefts. The stroma of this second tumor was highly cellular. There was a sharp delimitation between both tumors, with no transitional area. Immunochemistry demonstrated they are different tumor. A diagnosis of clear cell hidradenoma–basal cell carcinoma collision was performed. To the best of our knowledge, this is the first description of this challenging association. Copyright © 2020 Wolters Kluwer Health, Inc. All rights reserved.