Non-Hematopoietic Stem Cell Transplantation Treatment of Juvenile Myelomonocytic Leukemia: A Retrospective Analysis and Definition of Response Criteria

Background. Juvenile myelomonocytic leukemia (JMML) is a rare myeloproliferative disease of infancy. Allogeneic hematopoietic stem cell transplantation (HSCT) is currently the only curative treatment modality, while the role of anti-leukemic therapy prior to HSCT is uncertain. A comparative evaluation of the efficacy of different clinical protocols and great variety of anti-neoplastic drugs applied pre-HSCT is hampered by the lack of uniform criteria of response. Classification schemas applied in other forms of leukemia are of little value, because in JMML therapy may result in divergent responses in solid organs compared to peripheral blood (PB). Procedure. We therefore defined separate response criteria for white blood count (WBC), platelet count, liver size, and spleen size. We then retrospectively evaluated the efficacy of 129 treatment courses other than HSCT administered to 63 children with JMML. Treatment consisted of intensive therapy according to AML-type chemotherapy, maintenance-type combination therapy, and single agent therapy. To account for the variability observed in the natural course of disease, we also evaluated 32 episodes of "no therapy." Results. Best responses within 3 months of initiation of therapy were highly variable for the four response criteria. In contrast to platelet count and liver size, there was a significant correlation between WBC or spleen size and therapy. Response rates for WBC and spleen size were best for purine analogs, etoposide, and cytarabine as single agents or for maintenance-type combination therapy. Conclusion. To rigorously test future therapeutic strategies in this rare disease an international consensus on the definition of response criteria will be helpful.