Within the International Registry of Childhood Chronic Myeloid Leukemia (CML), we identified 18 patients less than 18 years old at diagnosis of CML who were in the chronic phase and exhibiting a sustained deep molecular response (DMR) to imatinib defined as BCR-ABL1/ABL1 < 0.01% (MR⁴) for at least two years followed by discontinuation of imatinib. Before discontinuation, the median duration of imatinib was 73.2 months (range, 32–109) and the median duration of MR⁴ was 46.2 months (range, 23.9–98.6). Seven patients experienced loss of major molecular response (MMR) 4.1 months (range, 1.9–6.4) after stopping and so restarted imatinib. The median molecular follow-up after discontinuation was 51 months (range, 6–100) for the nine patients without molecular relapse. The molecular free remission rate was 61% (95% CI, 38–83%), 56% (95% CI, 33–79%) and 56% (95% CI, 33–79%) at 6, 12 and 36 months, respectively. Six of the seven children who experienced molecular relapse after discontinuation regained DMR (median, 4.7 months; range, 2.5–18) after restarting imatinib. No withdrawal syndrome was observed. In univariate analysis, age, sex, Sokal and ELTS scores, imatinib treatment and DMR durations before discontinuation had no influence on treatment free remission. These data suggest that imatinib can be safely discontinued in children with sustained MR⁴ for at least two years.

Infant acute myeloid leukemia (AML) is a rare subgroup of AML of children <2 years of age. It is as frequent as infant acute lymphoblastic leukemia (ALL) but not clearly distinguished by study groups. However, infant AML demonstrates peculiar clinical and biological characteristics, and its prognosis differs from AML in older children. Acute megakaryoblastic leukemia (AMKL) is very frequent in this age group and has raised growing interest. Thus, AMKL is a dominant topic in this review. Recent genomic sequencing has contributed to our understanding of infant AML. These data demonstrated striking features of infant AML: fusion genes are able to induce AML transformation without additional cooperation, and unlike AML in older age groups there is a paucity of associated mutations. Mice modeling of these fusions showed the essential role of ontogeny in the infant leukemia phenotype compared to older children and adults. Understanding leukemogenesis may help in developing new targeted treatments to improve outcomes that are often very poor in this age group. A specific diagnostic and therapeutic approach for this age group should be investigated.