FISH detected 11q23 microdeletion and translocation at the long arm of chromosome 11 in a child with normal karyotypic acute lymphoblastic leukemia

We report on a 6-year-old girl with acute lymphoblastic leukemia (ALL) with 11q23 microdeletion and translocation at the long arm of chromosome 11, which were detected by fluorescence in situ hybridization (FISH) but not by conventional cytogenetics. She was hospitalized because of fever and generalized bone pain. Results of peripheral blood examination included a WBC of 5,400/microliter with 12% lymphoblasts. Bone marrow studies showed 75% of early pre-B lineage lymphoblasts with L1 morphology. G-banding chromosome analysis demonstrated a normal karyotype. However, FISH using mixed lineage leukemia (MLL) and 11q subtelomere probes demonstrated 11q23 microdeletion and translocation at the long arm of chromosome 11 to an undefined chromosome. MLL rearrangement was not detected by Southern blotting analysis. The patient achieved complete remission 15 days after receiving high-risk group chemotherapy of the Kyoto University Pediatric Hematology/Oncology Study Group and has remained in complete remission for more than 30 months. Since MLL/11q23 abnormalities confer a poor prognosis in childhood ALL, the accurate detection of such abnormalities is of paramount significance in assigning individual cases to risk categories. The findings from the present case and recent literature indicate that the FISH-based approach is complementary to conventional cytogenetics, and should be systematically used in childhood ALL at diagnosis.