Intriguing observations were made in a new mouse model of Noonan syndrome [41] in which stromal mutations of Ptpn11 encoding the protein tyrosine phosphatase SHP2 fostered onset of juvenile myelomonocytic leukemia (JMML) which was previously deemed to be a cell-intrinsic defect [42,43]. This evidence concerns the gene PTPN11 and juvenile myelomonocytic leukemia.