Genomic landscape of a metastatic malignant proliferating tricholemmal tumor and its response to PI3K inhibition.

Proliferating tricholemmal tumors (PTTs) are rare benign neoplasms that arise from the outer sheath of a hair follicle. Occasionally, these PTTs undergo malignant transformation to become malignant proliferating tricholemmal tumors (MPTTs). Little is known about the molecular alterations, malignant progression, and management of MPTTs. Here, we describe the case of a 58-year-old female that had a widely metastatic MPTT that harbored an activating PIK3CA mutation and was sensitive to the PI3K inhibitor, alpelisib (BYL719). We review the available literature on metastatic MPTT, detail the patient's course, and present a whole genome analysis of this rare tumor.
Competing Interests: KBD has received consulting fees from Kadmon and was an invited speaker for Illumina. RGA has receivedconsulting fees from Icon Medical Imaging and GI Reviewers LLC. WGY serves as a consultant for Olympus. CML has served as a consultant for Pfizer, Astra Zeneca, Novartis, Genoptix, Sequenom, Clovis, ARIAD,Takeda, Blueprints Medicine, and Foundation Medicine; an invited speaker for Abbott and Qiagen; and has received research funding (to her university) from Novartis, Astra Zeneca, and Xcovery.