Calcified chondroid mesenchymal neoplasm: a rose by any other name would still smell as sweet

Abstract

Calcified chondroid mesenchymal neoplasms (CCMNs) are a heterogeneous tumours of bone and soft tissue characterised by the presence of fibronectin 1 (FN1) gene rearrangements, plasmacytoid mononuclear cells, multinucleated cells and extracellular matrix production. Classically presenting as enlarging masses within the distal extremities or temporomandibular joint, CCMNs exhibit a benign radiological appearance. CCMNs are commonly characterised by fusions between the FN1 gene and genes of the fibroblast growth factor receptor (FGFR) family, but more novel fusions such as PDGFRA::USP8 and COL1A2::MIR29B have also been described. Herein we present a case of CCMN arising within the proximal phalanx, with a FN1:FGFR2 fusion identified on RNA sequencing and review the clinicopathological, radiological and molecular findings associated with this newly described and often challenging entity.