Treatment Outcome of Children With Multisystem Langerhans Cell Histiocytosis: The Experience of a Single Children’s Hospital in Shanghai, China

: We reported the outcome of 150 children newly diagnosed with multisystem langerhans cell histiocytosis following a langerhans cell histiocytosis-II-based protocol (arm B). However, the continuation treatment was extended to 56 weeks and etoposide was omitted from the continuation treatment. Risk organ (RO) involvement was defined as: liver (≥3 cm with or without functional impairment); spleen (≥2 cm below the costal margin in the midclavicular line); hematopoietic system (hemoglobin <100 g/L, and/or white blood cell count <4.0×10/L, and/or platelets <100×10/L). The lungs are not considered a RO in the current study. For the 59 patients with RO involvement (RO+), the rapid response rate (week 6) was 61.0% and the 3-year overall survival 73.4%±5.9%. Rapid responders had a better 3-year survival rate than poor responders (90.9%±5.0% vs. 45.7%±11.0%, P<0.001). Ninety-one patients without RO involvement (RO-) had a relatively low 3-year cumulative reactivation rate (10.7%). No deaths occurred in this subgroup and the 3-year overall survival of RO- patients was 100%. Poor responders of RO+ patients had an extremely poor prognosis. An effective salvage therapy is essential for this high-risk group. The initial treatment intensity and duration of continuation therapy both impact disease reactivation in RO- patients.