The gene associated with the familial type of trichoepithelioma links to the short arm of chromosome 9. If altered, cellular proliferation may be upregulated because of a poorly functioning or absent tumor suppressor. Because of the presence of significant numbers of Merkel cells within the tumor nest and the detection of a sheath of CD34-positive dendrocytes around the tumor nests, it appears that trichoepithelioma differentiates toward or derives from hair structures, particularly the hair bulge. In cases of multiple lesions, it may be disfiguring because of the involvement of the face. Occurrence of multiple trichoepitheliomas is transmitted as an autosomal dominant trait.
Lesions first appear in childhood and gradually increase in number.
Ulceration is rare. In the autosomal dominant form, multiple TE may be present, usually on the nasolabial folds. Because of lessened expressivity and penetrance in men, most patients are women. Solitary giant trichoepithelioma presents as a large, polypoid lesion, usually in the lower trunk or in the gluteal area. Perform shave or small punch biopsy to allow a histologic diagnosis.