FGF23 and neoplasm: Of note, our patient’s serum creatinine remained normal during burosumab therapy; serum creatinine was 1.01 mg/dL with eGFR of 79 ml/min/1.73 m2 when PTH was at its peak level of 120 pg/mL Moreover, the finding of the temporal increase in serum PTH levels after the initiation of burosumab is consistent with the inhibitory effect of FGF23 on PTH secretion in the setting of tumor-induced osteomalacia.