High-dose thiotepa may induce inappropriate secretion of antidiuretic hormone syndrome (SIADH) during conditioning treatment for allogeneic stem cell transplantation.

We conducted a retrospective, single-center, observational cohort study in patients with inappropriate secretion of antidiuretic hormone syndrome (SIADH) induced by high-dose thiotepa during conditioning for allogeneic stem cell transplantation (allo-HSCT). Between May 2018 and December 2023, 431 patients underwent allo-HSCT. All patients who developed SIADH had received TBF conditioning, and the incidence of SIADH among TBF-treated patients was 7.3%. Despite its limitations as a retrospective study, this real-life analysis shows that hyponatremia with corresponding serum hypo-osmolality and persistent urinary sodium excretion is compatible with a diagnosis of SIADH in the presence of normovolemia. Fluid balance and electrolyte levels should be closely monitored during conditioning to ensure prompt detection of SIADH promptly and enable immediate treatment.