Trichilemmal carcinoma occurring in a lesion of solar keratosis

A case of trichilemmal carcinoma occurring in a lesion of solar keratosis was reported. A 92-year-old woman had an erythematous plaque on her face that contained a reddish nodule. Histological examination of the nodule revealed typical features of trichilemmal carcinoma accompanied by those of solar keratosis in the marginal zone. The histological features of the erythematous plaque corresponded with those of solar keratosis. However, in situ the carcinoma developed in the epithelium of a hair follicle as well as in the interfollicular epidermis in the lesion of solar keratosis. We considered it likely that bowenoid malignant transformation occurred in both interadnexal and adnexal epithelium because of actinic damage, and a trichilemmal carcinoma arose. The paper also discussed the histogenesis of trichilemmal carcinoma.