Letter to the Editor Diagnostic Hematology A Rare Case of Pediatric T Lymphoblastic Leukemia With t(11;17)(q23;q21) Involving Mixed-Lineage Leukemia Gene Rearrangement

T lymphoblastic leukemia (T-ALL) comprises 10-15 % of pediat-ric ALL cases and is known to be a clinically and genetically heterogeneous disease [1]. Recent studies have presented vari-ous cytogenetic abnormalities in T-ALL. The alterations often present as reciprocal translocations implicated in several tran-scriptional factor genes and lead to arrest during T-cell differen-tiation [1, 2]. Although cytogenetic aberrations are known to be critical in leukemogenesis of many hematologic malignancies, the relationships between these aberrations and the prognosis are not well understood in T-ALL except for t(11;19), a mixed-lineage leukemia gene (MLL)-ENL fusion related to favorable prognosis [3]. Here, we report a very rare case of pediatric T-ALL with t(11;17)(q23;q21) involving MLL rearrangement, which has not been previously reported in Korea. A 16-month-old boy was admitted to our hospital because o