Infant acute lymphoblastic leukemia with t(11;16)(q23;p13.3) and lineage switch into acute monoblastic leukemia

Rearrangements of the mixed-lineage leukemia (MLL) gene have been associated with a poor prognosis in infant acute lymphoblastic leukemia (ALL). Previously, MLL translocations involving the CREP-binding protein (CREBBP) gene at chromosome band 16p13.3 have primarily been reported in treatment-related acute myeloid leukemia, after chemotherapy for other primary malignancies using topoisomerase II inhibitors. We report a case of de novo infant ALL with t(11;16)(q23;p13.3). After chemotherapy, this patient developed an acute monoblastic leukemia (M5b) with retention of the t(11;16)(q23;p13.3), indicating that this is a lineage switch of the original leukemic clone. To our knowledge, these findings have not been previously reported.