Early response to chemotherapy in children with Langerhans cell histiocytosis predicts long-term disease-free survival

Background: Langerhans cell histiocytosis (LCH) is a rare clonal malignancy of the monocyte-macrophage system. Patients with lesions in "risk organs" have significantly higher risk of mortality than patients with lesions limited to "non-risk" sites. The influence of early response to therapy on long-term survival in this heterogeneous multi-system disease was analyzed. Methods: During a 7-year period, we retrospectively analyzed the findings in 24 consecutive patients who required systemic chemotherapy for LCH [single system with multifocal bone involvement and multisystem involvement with or without risk organ (RO) involvement]. All patients were started on vinblastine and prednisolone. Progressive disease was treated with salvage protocols or targeted therapy. Positron emission tomography-computed tomography (PET-CT)/conventional CT based response assessment was performed at week 6 of chemotherapy, and if needed after week 12 of chemotherapy. Results: MFO bone, MS ROneg, and MS ROpos LCH was observed in 3, 4, and 17 patients, respectively. Age range of patients varied from 1 month-7 years (median = 18 months). The EFS and OS were 100% and 100% for MFO bone, 50% and 100%, respectively, for MS ROneg and 35% and 52%, respectively, for MS ROpos. OS was 93% and 100% for CR attained at 6 and 12 weeks respectively regardless of the risk status (P < 0.01). Conclusion: Rapid early response, that is, complete remission at 6 and 12 weeks was associated with significantly improved overall survival. In slow responders, early salvage with alternative regimens or targeted therapy may result in better outcomes.