PB2378 ALLOGENEIC STEM CELL TRANSPLANTATION EXPERIENCE IN JUVENILE MYELOMONOCYTIC LEUKEMIA

Background: Juvenile myelomonocytic leukemia (JMML) is a rarely seen clonal myeloproliferative disease in early childhood. White blood cell and monocyte elevation, hepatosplenomegaly, anemia, thrombocytopenia, hemoglobin F height is observed, 1.2 million per year is seen. Allogeneic stem cell transplantation is the definitive treatment method. Aims: In our clinic, nine patients with JMML were diagnosed in the last seven years. Mutation results; PTPN‐11 mutation in two patients, NRAS mutation in five patients, neurofibromatosis type 1 in one patient, and Noonan syndrome phenotype in one patient could not be obtained. Two of them have not yet been transplanted. A patient was planned to be transported at the external center in the late period, but was lost to the procedure. Six of the patients underwent stem cell transplantation in our unit. Results were evaluated. Methods: Five of the six patients underwent a single cell transplantation. A patient had to undergo two times of stem cell transplantation. The complaints of the patients were fever, rash and restlessness. The median age at admission was 24 months (3‐50 months), and the median admission period was 10 days‐17 months. The median number of white blood cells was 35 000 / mm3 (61120‐17920), the number of monocytes was 4200 / mm3 (1860‐6000), the number of platelets was 110 000 / mm3 (65000‐350 000), the hemoglobin level was 9 g / dl, the median hemoglobin F level 24% (3.2‐33.1) The median time from diagnosis to stem cell transplantation was median eight months (2‐10 months). In three of the patients, HLA was used as a fully suitable sibling donor and in four of them, the non‐consanguineous donor was used. Peripheral stem cell source was used in all of them. Myeloablative protocol including busulfan (0.8 mg / kg / dose, total16 doses, four days), melphalan (140 mg / m2 one day) and cyclophosphamide (120 mg / kg) was used as the patients preparation regime. Results: Neutrophil and platelet engraftment were obtained after transplantation. In chimerism, complete chimerism was achieved in four patients, and clinical and hematological improvement was observed. In one patient, 30% chimerism remained with decreased chimerism, and clinical and hematological remission was achieved. One patient had very low chimerism in the first month, and second transplantation was performed eight months later. The first and second month chimerism was obtained exactly. The median follow‐up period after transplantation was 26 months (two months‐80 months). All of our patients live without disease, 83% of our patients are in remission with a transplantation, only one has low chimerism, but is observed clinically and hematologically in remission. One of our patients (17%) required a second transplant and a complete remission was achieved. Summary/Conclusion: JMML is a rare type of chronic leukemia in childhood. It is necessary to prepare patients for allogeneic stem cell transplantation by early diagnosis and carrying a mutation study and carrying a specific mutation. If the transplant is planned and done in the early period, the chance of cure is high. Relapses after transplant can be seen around 50%. The second transplant should be planned in the early period. Early diagnosis and early transplantation of our JMML patients in our unit had a favorable effect on the results.