proliferating trichilemmal cyst proliferating trichilemmal cyst proliferating trichilemmal cysts (also known as a "pilar tumor", "proliferating follicular cystic neoplasm", "proliferating pilar tumor", and "proliferating trichilemmal tumor") are a cutaneous condition characterized by proliferations of squamous cells forming scroll-like structures.: 678 proliferating trichilemmal cystother namesproliferating pilar cyst proliferating tricholemmal (pilar) cyst