This case underscores the importance of intact FGF-23 testing for accurate TIO diagnosis, the diagnostic clue of hypophosphatemia with low/inappropriately normal 1,25 Vit D, the value of phosphate homeostasis knowledge, and prompt burosumab initiation when tumors are elusive or detected but inoperable (e.g., due to location not amenable to surgery). The gene discussed is FGF23; the disease is hypophosphatemia.