Double and single mixed-lineage leukemia-rearranged subclones in pediatric acute myeloid leukemia: a case report

BACKGROUND: Acute myeloid leukemia (AML) is a disease with a significant amount of cytogenetic heterogeneity including mixed-lineage leukemia (MLL) gene rearrangements. Pediatric AML commonly has genetic rearrangements which involve chromosome 11q23 in 15–20% of cases, and these genetic abnormalities have been associated with a poorer prognosis (Grimwade et al. in Blood 92:2322–2333, 1998; Raimondi et al. in Blood 94:3707–3716, 1999; Lie et al. in Br J Haematol 122: 217–225). MLL rearrangements in AML have been shown to have multiple different fusion partners (Meyer et al. in Leukemia 23:1490–1499). Heterogeneity of these cytogenetic abnormalities makes it difficult to determine how to approach patients from a treatment standpoint. This difficulty is further complicated when patients have more than a single MLL rearrangement. CASE PRESENTATION: A 10-year-old Caucasian girl presented with easy bruising and was found to have acute myeloid leukemia. Her cytogenetics showed two different MLL rearrangements, t(9;11)(p22;q23) and t(11;19)(q23;p13.3). At initial presentation she had no other cytogenetic findings. She responded well to initial therapy and achieved remission following the first induction cycle and completed four rounds of chemotherapy. She subsequently had a relapse of her AML, and her cytogenetics were consistent with a single MLL rearrangement, t(9;11)(p22;q23), in addition to monosomy 7. She was treated with reduction therapy and a haplo-identical bone marrow transplant but ultimately succumbed to her disease. CONCLUSION: MLL rearrangements are common in AML, but clinical significance continues to be elusive, and there is conflicting data on the prognostic significance. In the setting of multiple MLL rearrangements, there is concern for reduced survival, although treatment modifications are not currently done in this setting. This report details a case with multiple MLL rearrangements that initially responded to therapy but ultimately had disease progression with a selection of a leukemic clone containing a single MLL rearrangement.