Transient juvenile myelomonocytic leukemia in the setting of PTPN11 mutation and Noonan syndrome with secondary development of monosomy 7.

Juvenile myelomonocytic leukemia (JMML) is a rare childhood neoplasm with poor prognosis except in the setting of Noonan syndrome, where prognosis is generally favorable. We present the case of a child with JMML in the setting of germline PTPN11 mutation and Noonan syndrome with suspected secondary development of monosomy 7 in the bone marrow. Diagnosed shortly after birth, she has been managed with active surveillance alone. Myeloblast percentages initially fluctuated; however, bone marrow biopsy at 4 years of age showed spontaneous remission despite persistence of the monosomy 7 clone, supporting a cautious approach in similar cases.