Basaloid skin tumours: Mimics of basal cell carcinoma

SummaryThis article is the second of two papers relating to the histopathological diagnosis of basaloid skin tumours and the uses of immunohistochemistry. The first paper focused on basal cell carcinoma and variants, and this paper will concentrate on tumours that may be confused with basal cell carcinoma. The basaloid tumours of the skin can be classified according to the general classification of skin tumours, including epidermal, appendageal (hair follicle and sweat gland derived) and others including cutaneous metastases. The areas of discussion concentrate on the distinction of basal cell carcinoma from basaloid squamous cell carcinoma, infiltrative basaloid tumours (desmoplastic trichoepithelioma, infiltrative basal cell carcinoma, microcystic adnexal carcinoma and eccrine epithelioma), follicular induction overlying dermatofibroma, basaloid proliferations in naevus sebaceus, trichoepithelioma, trichoblastoma, trichoepithelioma-like basal cell carcinoma, pilomatrical tumours and selected sweat gland tumours. The immunohistochemical stains that may be of use in differential diagnosis are discussed, including BerEP4, epithelial membrane antigen, CD10, bcl-2, Cam5.2, CK20, carcinoembryonic antigen and p53.