Fibronectin 1 (FN1)-rearranged Mesenchymal Neoplasms: An Updated Review

Fibronectin 1 (FN1), located on chromosome 2q35, encodes fibronectin, a high molecular weight glycoprotein of the extracellular matrix. Several histologically overlapping chondroid matrix-producing tumors are known to harbor FN1 rearrangements, including soft tissue chondroma, synovial chondromatosis, calcifying aponeurotic fibroma, calcified chondroid mesenchymal neoplasm and phosphaturic mesenchymal tumor. Over the past 10 years, fusions involving the FN1 gene have also been identified in other mesenchymal neoplasms such as lipofibromatosis and inflammatory myofibroblastic tumor. The current World Health Organization Classification of Soft Tissue and Bone Tumors suggests that FN1-rearranged lesions are typically benign or intermediate. This review provides an updated overview of the clinical, histological and molecular genetic features of FN1-rearranged mesenchymal neoplasms and discusses their relationships with one another.