LYMPHOID NEOPLASIA

MLL translocations in adult B-cell precur-sor (BCP) acute lymphoblastic leukemia (ALL) are largely restricted to the imma-ture CD10 immunophenotypes. MLL-AF4 is known to be the most frequent fusion transcript, but the exact frequen-cies of MLL aberrations in CD10 adult BCP-ALL are unknown. We present a genetic characterization of 184 BCR-ABL CD10 adult ALL cases (156 cyIg, 28 cyIg) diagnosed between 2001 and 2007 at the central diagnostic laboratory of the GMALL study group. Patient samples were investigated by RT-PCR for MLL-AF4, MLL-ENL, and MLL-AF9 and by long-distance inverse polymerase chain reaction, thus also allowing the identifica-tion of unknown MLL fusion partners at the genomic level. MLL-AF4 was detected in 101 (54.9%) and MLL-ENL in 11 (6.0%) cases. In addition, rare MLL fusion genes were found: 2 MLL-TET1 cases, not previ-ously reported in ALL, 1 MLL-AF9, 1 MLL-PTD, a novel MLL-ACTN4, and an MLL-11q23 fusion. Chromosomal breakpoints were determined in all 118 positive cases, revealing 2 major breakpoint cluster re-gions in the MLL gene. Characteristic features of MLL patients were signifi-cantly lower CD10 expression, expres-sion of the NG2 antigen, a higher white blood count at diagnosis, and female sex. Proposals are made for diagnostic as-sessment. The clinical studies are regis