Adipocyte-rich CTNNB1 -mutated Intramuscular Gardner Fibroma Progressing to Desmoid Fibromatosis

• Published in: Pediatric and developmental pathology Vol. 24; no. 1; p. 62
• Main Authors: Bakker, Andrea, Slack, Jonathan C, Caragea, Mara, Kurek, Kyle C, Bründler, Marie-Anne
• Format: Journal Article
• Language: English
• Published: United States 01.01.2021
• Subjects: b-catenin; soft-tissue; CTNNB1; desmoid fibromatosis; Gardner fibroma; pediatrics
• ISSN: 1615-5742
• DOI: 10.1177/1093526620968807

Gardner fibroma (GF) is a benign soft-tissue tumor that is associated with Gardner syndrome and can progress to, or co-occur with, desmoid fibromatosis (DF). Herein, we report a unique case of an 11-year-old boy who presented with a rapidly growing soft-tissue mass after biopsy of a stable fat-rich lesion present in the calf muscles since infancy, with Magnetic resonance imaging findings suggesting an intramuscular adipocytic tumor. The resection showed GF and DF. DF arising from a preexisting GF (the so-called "GF-DF sequence") is a well-documented phenomenon. Although immunohistochemistry was negative for nuclear β-catenin expression, a S45F mutation, which has been associated with aggressive behavior in DF, was identified in both components using a next-generation sequencing-based molecular assay. This is the first time a mutation in has been identified in GF and the GF-DF sequence, thus expanding our knowledge of the molecular pathogenesis of the GF-DF sequence and highlighting the role of molecular testing in pediatric soft-tissue tumors. The histologic findings of an adipocyte-rich intramuscular GF also are unique, expanding the morphological spectrum of GF and adding GF to the differential diagnosis of intramuscular lesions with an adipocytic component.