Pilar tumour: a distinctive type of trichilemmoma.

A series of pilar tumours is presented. Although they are predominantly tumours of the elderly female, they occur also in men and in middle age. Some 90 per cent occur on the scalp or nape of neck; about 10 per cent affect other areas. Most tumours outside the scalp involve the trunk; they are rare on the extremities. Evidence is presented that most arise from pre-existing pilar cysts. Two tumours recurred, but were cured by re-excision. Four tumours exhibited histological and/or cytological criteria of malignancy. Two of these were interpreted as in situ carcinomas, and two as combined invasive and in situ carcinomas. None is known to have metastasized or to have behaved aggressively. The prognosis of pilar tumours in excellent whatever the histological appearance. The nature of the lesion and the problems of nomenclature associated with it are discussed.