Role of colony-stimulating factor 1 in the neoplastic process of tenosynovial giant cell tumor

Tenosynovial giant cell tumors (TGCTs) are rare, locally aggressive, mesenchymal neoplasms, most often arising from the synovium of joints, bursae, or tendon sheaths. Surgical resection is the first-line treatment, but recurrence is common, with resulting impairments in patients’ mobility and quality of life. Developing and optimizing the role of systemic pharmacologic therapies in TGCT management requires an understanding of the underlying disease mechanisms. The colony-stimulating factor 1 receptor (CSF1R) has emerged as having an important role in the neoplastic processes underlying TGCT. Lesions appear to contain CSF1-expressing neoplastic cells derived from the synovial lining surrounded by non-neoplastic macrophages that express the CSF1R, with lesion growth stimulated by both autocrine effects causing proliferation of the neoplastic cells themselves and by paracrine effects resulting in recruitment of CSF1 R-bearing macrophages. Other signaling pathways with evidence for involvement in TGCT pathogenesis include programmed death ligand-1, matrix metalloproteinases, and the Casitas B-cell lymphoma family of ubiquitin ligases. While growing understanding of the pathways leading to TGCT has resulted in the development of both regulatory approved and investigational therapies, more detail on underlying disease mechanisms still needs to be elucidated in order to improve the choice of individualized therapies and to enhance treatment outcomes.