Proliferating trichilemmal tumour: diagnostic challenge on core biopsy.

A 70-year-old woman presented with a 10-month history of an irregular mass in the left lateral nape of her neck which had recently increased in size rapidly. Ultrasound-guided core needle biopsy was obtained, and the tumour was diagnosed as a well-differentiated squamous cell carcinoma. Further imaging studies failed to demonstrate additional malignant characteristics. In view of these findings, a wide local excision of the tumour was performed. Histopathological assessment of the resected tumour revealed a proliferating trichilemmal tumour with well-differentiated features and smooth invasion front. This article serves as an important reminder of the challenges associated with pathological evaluation of core needle biopsies of adnexal tumours. It emphasises the importance of clinical-radiological-pathological correlation preferably in a multidisciplinary team setting prior to agreeing on a definitive management plan. © BMJ Publishing Group Limited 2019. No commercial re-use. See rights and permissions. Published by BMJ.