Frequency, Characteristics, Management, and Outcomes of Posttransplant Lymphoproliferative Disorder After Allogeneic Hematopoietic Stem Cell Transplantation in Children: A Multicentre Retrospective Study of the Turkish Pediatric BMT Study Group

Objective: Posttransplant lymphoproliferative disorder (PTLD) is a rare yet potentially life-threatening complication following allogeneic hematopoietic stem cell transplantation (HSCT). This study aimed to determine the incidence, clinical features, management strategies, and prognostic factors influencing outcomes of PTLD after allogeneic HSCT in children. Materials and Methods: Data were retrospectively collected from 15 pediatric centers performing allogeneic HSCT between June 2010 and May 2025. Clinical features, treatment approaches, and outcomes of the cases were analyzed. Results: During the study period, 6129 children underwent allogeneic HSCT and 34 (0.56%) developed PTLD. The median interval between HSCT and PTLD diagnosis was 197 days, with the majority of cases occurring within the first posttransplant year. At diagnosis, gastrointestinal involvement was observed in 22 patients (64.7%), cytopenia in 17 (50%), central nervous system (CNS) involvement in 7 (20.5%), pulmonary involvement in 6 (17.6%), and macrophage activation syndrome in 4 (11.7%). Rituximab-based therapy was administered to 29 patients (85.3%) and immunosuppression was reduced in 25 (73.5%). Mortality was significantly higher among patients presenting with CNS involvement (4 of 7, 57.1%; p