Proliferating trichilemmal tumor: report of a case and review of the literature. The authors report a case of proliferating trichilemmal tumor and review the related literature. Although considered biologically benign, malignant proliferating trichilemmal tumor have been reported. The authors emphasize the importance of recognizing that the tumors can occur in individuals in their 20s and 30s, and that the tumors should be excised with a margin of normal tissue. Routine follow-up is recommended. 