Haematopoietic stem cell transplantation for refractory Langerhans cell histiocytosis: outcome by intensity of conditioning

Summary Patients with Langerhans cell histiocytosis ( LCH ) refractory to conventional chemotherapy have a poor outcome. There are currently two promising treatment strategies for high‐risk patients: the first involves the combination of 2‐chlorodeoxyadenosine and cytarabine; the other approach is allogeneic haematopoietic stem cell transplantation ( HSCT ). Here we evaluated 87 patients with high‐risk LCH who were transplanted between 1990 and 2013. Prior to the year 2000, most patients underwent HSCT following myeloablative conditioning ( MAC ): only 5 of 20 patients (25%) survived with a high rate (55%) of transplant‐related mortality ( TRM ). After the year 2000 an increasing number of patients underwent HSCT with reduced intensity conditioning ( RIC ): 49/67 (73%) patients survived, however, the improved survival was not overtly achieved by the introduction of RIC regimens with similar 3‐year probability of survival after MAC (77%) and RIC transplantation (71%). There was no significant difference in TRM by conditioning regimen intensity but relapse rates were higher after RIC compared to MAC regimens (28% vs. 8%, P = 0·02), although most patients relapsing after RIC transplantation could be salvaged with further chemotherapy. HSCT may be a curative approach in 3 out of 4 patients with high risk LCH refractory to chemotherapy: the optimal choice of HSCT conditioning remains uncertain.