Tumors of the pilosebaceous unit

Appendage tumors of the pilosebaceous apparatus are relatively rare, and their clinical aspect is usually nonspecific. In most cases pilosebaceous tumors are benign; however, malignant neoplasias (e.g. trichilemmal carcinoma, malignant pilomatricoma) have been described. In the present review we propose the classification of pilosebaceous tumors by degree and by direction of differentiation and by histological configuration. Three different histological patterns have to be distinguished: tumors with central dilated hair follicle, tumors consisting of epithelial islands and keratotic cysts in the corium and neoplasias with predominantly mesenchymal components surrounding epithelial formations. Careful histopathological examination of pilar appendage tumors will help to classify the wide range of clinically and histologically different tumors and to establish the exact diagnosis.