In 50 well-characterized phosphaturic mesenchymal tumours, excessive FGF23 production was attributable to a fibronectin (FN1)–FGFR1 fusion gene in 21 (42%) tumours and in 3 (6%) to a FN1-FGF1 fusion gene [319,321]. Here, FGFR1 is linked to neoplasm.