The watch-and-wait approach for patients with juvenile myelomonocytic leukemia: results of the French cohort.

Juvenile myelomonocytic leukemia (JMML) is a rare, aggressive pediatric myeloproliferative neoplasm for which hematopoietic stem cell transplantation (HSCT) is currently the only established curative therapy. However, a watch-and-wait (W&W) approach has shown promise for long-term survival in selected cases. In this real-world study, we analyzed outcomes of patients with JMML initially managed with a W&W strategy within a nationwide cohort of 161 genetically characterized cases. W&W was chosen for 35 patients, with increasing adoption over time, reaching 39% in the 2016-to-2021 period. Most patients carried mutations in CBL (43%), NRAS (34%), or homozygous germ line SH2B3 (14%). Over a median follow-up of 6.5 years, 30 of 35 (86%) achieved long-term survival with partial or complete resolution of myeloproliferative symptoms, although clonal hematopoiesis persisted in nearly all survivors (18/20). Disease progression occurred in 5 patients (CBL, n = 3; NRAS, n = 1; PTPN11, n = 1), mostly within 2 years after diagnosis. Overall, in the W&W cohort, the 5-year overall and event-free survivals were 93.1% and 84.5%, respectively. In NRAS-mutated cases, age of <30 months, normal to slightly elevated fetal hemoglobin, platelet counts of >45 × 109/L, the absence of additional somatic mutations, and low DNA methylation profile were associated with favorable outcomes. In CBL-driven JMML, no predictive factor of adverse evolution was identified. Notably, W&W was effective in all patients with homozygous germ line SH2B3. These findings support W&W as a viable alternative in up to 30% of patients with JMML, potentially sparing them from HSCT-associated risks. Given the persistence of clonal hematopoiesis and the risk of extrahematological complications, long-term monitoring remains essential.