In vivo xenotransplantation into NSG and/or NSG-S mice of samples from 15 JMML cases covering the most frequent genetic subgroups (i.e., PTPN11, NRAS, and KRAS) confirmed the capacity of most JMML samples to engraft in immunodeficient mice [14, 16]. This evidence concerns the gene KRAS and juvenile myelomonocytic leukemia.