Proliferating trichilemmal tumour

Cutaneous cysts represent a large proportion of the specimens submitted for histopathological examination and comprise a wide spectrum of entities. The less common keratinous cysts are of pilar or trichilemmal type and proliferating trichilemmal tumour is infrequent. Transitional changes between an ordinary trichilemmal cyst and proliferating trichilemmal (pilar) tumour are seen. These usually behave in a benign fashion according to their bland cytology and architecture, although occasional examples with frank malignancy have been reported, simulating squamous cell carcinoma. This paper reports two cases representing the full range in the spectrum of proliferating trichilemmal tumour, underlining the need to distinguish these lesions from squamous cell carcinoma of the head and neck region and highlighting difficulties regarding their terminology.