FGF18 is a pleiotropic growth factor that regulates cell proliferation, differentiation, and migration through fibroblast growth factor receptor (FGFR) signaling 1. This 207 amino acid glycosylated protein is widely expressed in developing and adult tissues including bone, lung, brain, heart, and mesenchyme 1. FGF18 plays critical roles in skeletal development and homeostasis, with FGF18 knockout mice exhibiting perinatal lethality characterized by cleft palate, curved long bones, deformed ribs, and reduced body size 1. In cartilage homeostasis, FGF18 promotes chondroanabolic activity and has emerged as a validated osteoarthritis (OA) therapeutic target 2. AAV2-FGF18 gene therapy reduces cartilage defect size by up to 76% and increases cartilage thickness by up to 106% in OA models, while preventing subchondral bone collapse 3. Conversely, FGF18 promotes pathological fibrosis in other contexts; hepatocyte-derived FGF18 stimulates hepatic stellate cell proliferation via Ccnd1 upregulation, driving liver fibrosis progression 4. FGF18 is associated with multiple cancers including breast, lung, and ovarian malignancies 1. These dual roles highlight FGF18's tissue-dependent functions and its potential as a selective therapeutic target for OA while requiring caution in fibrosis-prone tissues.