BACKGROUND: A proliferating trichilemmal cyst (PTC) is an uncommon, rapidly-reproducing cutaneous epithelial cyst, differentiating from the isthmic portion of the outer hair root sheath. It is usually described as a benign tumor, but malignant transformation has been reported and is then denominated as a malignant proliferating trichilemmal tumor. Ki67 immunostaining has been used as a methodology for the evaluation of tumor grade in other tumors, due to its distinctive reaction patterns which exclusively involve proliferating cells. OBJECTIVES: (1) To report the incidence of cases of PTCs in a General Hospital during a 12 years period. (2) To determine the expression of ki67 using immunohistochemical staining. (3) To correlate ki67 reaction patterns with clinical prognosis. MATERIALS AND METHODS: The dermatology department's files during a period of 12 years were reviewed; cases with a diagnosis of PTC were selected, and ki67 immunostaining was done when enough biological material was available. RESULTS: A total of 15 cases with a diagnosis of PTC were identified. In 12 cases, ki67 immunostaining was carried out. In 9 of the 12 cases, ki67 was observed in the basal cells of the cystic epithelium, one case was moderately positive in palisading epithelial cells; in the other two cases ki67 immunostaining was negative. Clinical follow-up was done and revealed that no patient had local recurrence in 5 years after surgical removal of PTC. We therefore consider this immunostaining technique is probably correlated with low recurrence potential.
