The fusion transcripts of MLL rearrangement [MLL( þ )] in acute myeloid leukemia (AML) and their clinicohematologic correlation have not be well characterized in the previous studies. We used Southern blot analysis to screen MLL( þ ) in de novo AML. Reverse transcriptase-polymerase chain reaction was used to detect the common MLL fusion transcripts. cDNA panhandle PCR was used to identify infrequent or unknown MLL partner genes. MLL( þ ) was identified in 114 (98 adults) of 988 AML patients. MLL fusion transcripts comprised of 63 partial tandem duplication of MLL (MLL-PTD), 14 MLL-AF9, 9 MLL-AF10, 9 MLL-ELL, 8 MLL-AF6, 4 MLL-ENL and one each of MLL-AF1, MLL-AF4, MLL-MSF, MLL-LCX, MLL-LARG, MLL-SEPT6 and MLL-CBL. The frequency of MLL-PTD was 7.1% in adults and 0.9% in children (Po0.001). 11q23 abnormalities were detected in 64% of MLL/t11q23 and in none of MLL-PTD by conventional cytogenetics. There were no differences in remission rate, event-free survival and overall survival between adult MLL-PTD and MLL/t11q23 groups. Adult patients had a significantly poorer outcome than children. The present study showed that cDNA panhandle PCR can identify all rare or novel MLL partner genes. MLL-PTD was rare in childhood AML. MLL( þ ) adults had a poor outcome with no difference in survival between MLL-PTD and MLL/t11q23 groups.

The role of internal tandem duplication of fms-like tyrosine kinase 3 (FLT3/ITD), mutations at tyrosine kinase domain (FLT3/ TKD) and N-ras mutations in the transformation of myelodysplastic syndrome (MDS) to AML was investigated in 82 MDS patients who later progressed to AML; 70 of them had paired marrow samples at diagnosis of MDS and AML available for comparative analysis. Five of the 82 patients had FLT3/ITD at presentation. Of the 70 paired samples, seven patients acquired FLT3/ITD during AML evolution. The incidence of FLT3/ITD at diagnosis of MDS was significantly lower than that at AML transformation (3/70 vs 10/70, Po0.001). FLT3/ITD( þ ) patients progressed to AML more rapidly than FLT3/ITD(À) patients (2.570.5 vs 11.971.5 months, P ¼ 0.114). FLT3/ITD( þ ) patients had a significantly shorter survival than FLT3/ITD(À) patients (5.671.3 vs 18.071.7 months, P ¼ 0.0008). After AML transformation, FLT3/ITD was also associated with an adverse prognosis. One patient had FLT3/TKD mutation (D835Y) at both MDS and AML stages. Additional three acquired FLT3/TKD (one each with D835 H, D835F and I836S) at AML transformation. Five of the 70 matched samples had N-ras mutation at diagnosis of MDS compared to 15 at AML transformation (Po0.001), one lost and 11 gained N-ras mutations at AML progression. Coexistence of FLT3/TKD and N-ras mutations was found in two AML samples. N-ras mutations had no prognostic impact either at the MDS or AML stage. Our results show that one-third of MDS patients acquire activating mutations of FLT3 or N-ras gene during AML evolution and FLT3/ITD predicts a poor outcome in MDS.

The roles of CEBPalpha mutations and its cooperating mutations in the relapse of acute myeloid leukemia (AML) are not clear. CEBPalpha mutations were analyzed on 149 patients with de novo AML at both diagnosis and relapse. Twenty-two patients (14.8%) had the mutations at diagnosis, two patients had N-terminal nonsense mutations alone, one had homozygous inframe duplication at the bZIP domain, and 19 patients had both N-terminal and bZIP mutations. Twenty patients relapsed with identical mutant patterns, two lost CEBPalpha mutations and none acquired the mutations at relapse. Cloning analysis showed that the N-terminal and C-terminal mutations occurred on separate cloned alleles and also on the same alleles in most of the diagnosis and relapse samples. Losing one of the two or more mutations on the same allele or acquiring the other mutation on the allele original carrying single mutation were observed not infrequently in the paired samples analyzed. Seven patients with CEBPalpha mutations had cooperating mutations with FLT3/ITD, FLT3/TKD or N-ras but not K-ras mutations. Our study showed that 91% of de novo AML harboring CEBPalpha mutations at diagnosis retained the identical mutant patterns but frequently changed in the allelic distribution at relapse.

The present study showed that apart from EEC assay, the post-phlebotomy serum EPO level was a sensitive and specific parameter in the differential diagnosis of polycythaemia, in particular for the identification of PV among patients with unclassifiable polycythaemia.