Abstract Background In pediatric multi-system high risk organs (RO +) Langerhans cell histiocytosis (LCH), failing 1st line treatment has the highest mortality. We aim to present the outcome of failure of 1st line whether due to disease progression (DP) at end of induction or reactivation (REA) after initial better status response. Patients and methods Sixty-seven RO + LCH patients with hemopoietic, hepatic or splenic involvement, treated between 2007 and 2019 were retrospectively analyzed. The median follow-up (IQR) is 6 years (4–8.8 y).They were subjected to 2 eras of treatment; one with salvage by 2-Cda based regimen (2-CdABR) and another without. Results Of 67 patients, M/F 40/27, median age 1.74 y (0.2–10 y), 42 failed 1st line (62.7%). Of them DP n = 22 (52%) and REA n = 20 (48%). Of those with DP, 9/22 patients received 2-CdABR, where 5 survived in better status. While the remaining 13 did not receive 2-CdABR and all of them died. Otherwise, of those with REA, 12/20 reactivated on RO + mode. Of them, 8/12 received 2-CdABR, where only one survived in better status and the remaining 4 received vinblastine-based regimen,where 2 died and 2 were rescued. RO + 5-year overall survival (OS) was 65% (CI 95% 54 -78) while the event free survival (EFS) 36% (26.3—50.1). The OS of DP 27% (14–54) versus REA 67% (49–93) p 0.004. OS of DP with 2-CdABR 56% (31–97.7) versus 8% without (2–51), p &lt; 0.001. While OS of REA with 2-CdABR 38% (13–100) versus 74% without (53–100) p 0.7. Conclusion Survival of RO + remains limited. Failure of 1st line in RO + due to DP carries worse prognosis in relation to REA. In DP those who were not salvaged by 2-CdABR, showed dismal outcome. This could not be shown when applied in REA.

High risk Langerhans cell histiocytosis in children: the role of salvage in improving the outcome. A single center experience