Trichoepithelioma with an adjacent basal cell carcinoma, transformation or collision?

Trichoepitheliomas (TEs) are benign follicular neoplasms that can be difficult to separate histologically from basal cell carcinomas (BCCs). It is important to make this distinction, because the treatments and prognoses differ for the two lesions. Previous reports have employed both histologic and immunohistochemical data in order to separate these two lesions. It is believed that transformation from a TE to a BCC is a rare event. We describe a case in which a single lesion with features of TE and BCC is present in a patient with multiple lesions of BCC.