A case of FN1-fused calcified chondroid mesenchymal neoplasm of the hand with novel FGFR3 partner gene.

Calcified chondroid neoplasms with FN1::FGFR1 or FGFR2 constitute a recently described category of mesenchymal neoplasms mostly encountered in the extremities and temporomandibular joint. Herein, we report a case of FNI1-fused calcified chondroid neoplasm of the hand with a novel FGFR3 fusion partner. The tumor exhibited a multilobulated growth pattern composed of epithelioid cells embedded in abundant stroma with myxoid, chondroid and fibrous areas and scattered osteoclast-like giant cells. RNA sequencing revealed an in-frame fusion between exon 31 of FN1 and exon 3 of FGFR3, which was subsequently confirmed by reverse transcription-polymerase chain reaction. Our findings expand on the spectrum of potential fusion partners in FN1-fused calcified chondroid neoplasms. This article is protected by copyright. All rights reserved.