Citrulline-containing basal cell carcinomas. Differentiation toward hair structures with induction of dermal hair papillae

Abstract

Citrulline is demonstrable histochemically only in keratin which is derived from either the inner root sheath or medulla of hair follicles. All other keratins, including epidermal keratin, are negative for citrulline. Keratotic basal cell carcinomas occasionally contain citrulline in their keratin. Of high statistical significance is the greater mean rated value for the presence of dermal hair papilla-like structures among keratotic citrulline (+) tumors than among keratotic citrulline (-) ones. The presence of citrulline (+) keratin (inner root sheath keratin) in a tumor along with hair papilla-like structures in the adjacent dermis indicate an attempt of the tumor to recapitulate normal hair growth. Such findings reflect a high degree of differentiation of these tumors and rule out the possibility of their being squamous carcinomas. These two differential diagnostic aids may be of some practical value in difficult diagnostic decisions between keratinizing basal cell and keratinizing squamous cell carcinomas. They should also help to diminish the number of tumors relegated to the general category of “basosquamous carcinomas”.