OBJECTIVETo explore a rapid, sensitive and effective method for identifying 11 q23/MLL gene rearrangements and investigate the incidence and clinical features of adult acute leukemia (AL) patients with 11 q23/MLL abnormalities.

METHODSBone marrow samples from 112 adult AL patients were prepared by short-term (24 hours) unstimulated culture, and karyotyped by R-banding. The abnormal signals were screened by interphase- fluorescence in situ hybridization (FISH) with dual-color break-apart 11 q23/MLL-specific probe, and the 11 q23/MLL gene rearrangements were determined by metaphase-FISH.

RESULTSOf the 112 patients,9 (8. 0%) with 11q23/MLL translocations were revealed by FISH, among which only 4 (3. 6% ) was revealed by CCA. Three patients were reported by CCA to have del( 11) ( q23) , while by FISH assay two of them were 11 q23/MLL translocation and one was true deletion of I lq23 telomeric terminus. Furthermore by FISH assay II q23/MLL translocations were identified in one each patient with normal karyotype, with 11 q + and without overt 11 q23 abnormality. Eight patients with MLL gene amplification including polysome, homogenous staining region (hsr) and double minute chromosome (dmin) were also disclosed by FISH. AL patients with 11 q23/MLL abnormalities were frequently diagnosed as pro-B acute lymphoblastic leukemia (pro-B ALL) ,acute monocytic leukemia (AMoL) or biphenotypic acute leukemia (BAL).

CONCLUSIONFISH with dual-color break-apart I q23/MLL -specific probe is a rapid and sensitive method to detect 11 q23/MLL abnormalities, as compared with CCA. FISH also effectively discloses translocations and amplifications involving 11 q23/MLL,and should be performed in patients diagnosed as pro-B ALL,AMoL or BAL, with CCA normal karyotype.