Trichilemmomas show loss of PTEN in Cowden syndrome but only rarely in sporadic tumors

Background: Trichilemmoma (TL) can occur as a solitary sporadic lesion usually on the face or as multiple facial lesions almost invariably associated with Cowden syndrome (CS). CS is a multisystem disorder caused by a germline inactivating mutation in PTEN (10q23.31), a tumor suppressor gene. We sought to identify PTEN loss by immunohistochemistry (IHC) in sporadic and CS-associated TL to determine whether IHC is a useful tool to assess an individual for CS. Methods: Six TL biopsies associated with CS and 33 biopsies without CS were retrieved. IHC for PTEN was performed. Results were scored as positive (reactivity in TL cells) or negative (no reactivity in TL cells); normal squamous epithelium and vascular endothelium served as internal positive controls. Results: Complete PTEN loss was noted in 5/ 6 (83%) CS-associated TL and 1/ 33 (3%) sporadic (non-CS) TL. Conclusion: Demonstration of complete PTEN loss in TL by IHC is strongly suggestive of association with CS, but retention of PTEN staining does not entirely exclude CS. Therefore, PTEN IHC in TLs may be helpful in screening TL for association with CS, but should be used in context with other established clinical criteria, and possibly germline PTEN genotyping to confirm a diagnosis of CS.