FGF23 and osteomalacia: In this paraneoplastic disease, the tumor secretes phosphaturic factors known as “phosphatonins” [1–3], amongst which fibroblast growth factor 23 (FGF23) is the most frequently found, leading to the cardinal features of the disease: hypophosphatemia from renal phosphate wasting, reduced 1,25-dihydroxyvitamin D concentration through inhibition of its synthesis, rickets in children and osteomalacia in adults, with diffuse bone pain, fractures and muscle weakness.