Clear Cell Hidradenoma—Basal Cell Carcinoma Collision

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.