A Rare Case of Multifocal Asynchronous Benign Granular Cell Tumors with PIK3CA Subclonal Mutation Identified in One Tumor by Next-Generation Sequencing

Granular cell tumor (GCT) is a benign neuroectodermal tumor typically in the dermis or subcutis, although deep soft tissues and organs are occasionally involved. Multifocal GCTs are estimated to occur as many as 10% of patients. A 40-year-old female presented with multiple GCTs asynchronously involving various body sites including gastrointestinal, gynecologic, breast, urinary, and soft tissue systems. Pathologic examinations suggested benign GCTs. TruSight Tumor 170 next-generation sequencing (NGS) analysis performed on four resected tumors revealed subclonal mutation of PIK3CA p.H1047R identified in the esophageal GCT but not in the right vulva or the two cecal GCTs, suggesting that each is a primary tumor with a distinct genetic profile, rather than metastasis. PIK3CA p.H1047R is a common mutation in many cancers. Our benign GCT case demonstrates PIK3CA mutation with a low mutant allele frequency of 7%, which may represent an evolving subclone and might confer a more aggressive behavior.