Case Report: Haemopoietic stem cell transplantation in refractory paediatric RAS-associated lymphoproliferative disorder.

RAS-associated lymphoproliferative disorder (RALD), caused by acquired gain-of-function mutations in Kirsten rat sarcoma KRAS or Neuroblastoma rat sarcoma NRAS, is an orphan disease with very few cases reported worldwide. The most common presenting feature is autoimmune cytopenia, which is generally documented to be responsive to immunosuppression. We describe two cases of RALD in which associated autoimmunity proved refractory to multiagent immunosuppression. We also share our experience of haematopoietic stem cell transplantation (HSCT) in the two patients with recalcitrant autoimmunity, adding valuable insight into the distinctive complications and transplant course in this rare disorder. Furthermore, we review the published literature on HSCT in RALD, which includes three other patients, primarily transplanted for malignant transformation of RALD. In addition, we report our experience with targeted therapy, specifically the MEK inhibitor, in this disease and reflect on its role within the treatment paradigm of RALD.