2.3. Follow-up
Progression (PD) before achieving complete remission (CR), relapse after CR, secondary cancer or Langenhans cell histiocytosis (LCH), and death due to any cause were evaluated as events. The criterion of PD, CR and stable disease (SD) was in consistence with the International Pediatric NHL Response Criteria.26 OS time was calculated from the time of initial diagnosis to death; event-free survival (EFS) time was from the time of initial diagnosis to the first event. Patients who had not died or experienced other events at final analysis were censored at the last follow-up in May 2020.