A phase 2, open-label, single-arm study evaluated the efficacy and safety of burosumab in adults (aged ≥18 years) with TIO not curable by surgical excision or with cutaneous hypophosphatemia syndrome (CSHS), a rare condition defined by the association of epidermal and/or melanocytic nevi, a mosaic skeletal dysplasia, and FGF23-mediated hypophosphatemia. Here, FGF23 is linked to hypophosphatemia.