Overexpression of BAALC and MN1 Predict Worse Outcome in De Novo AML with Partial Tandem Duplication of MLL.

Overexpression of BAALC, MN1, or ERG gene has been described to have adverse impact on the outcome of acute myeloid leukemia (AML) with normal karyotype. The majority of patients with partial tandem duplication of MLL gene (MLL-PTD) had normal karyotypes. The prognostic relevance of overexpression of these genes in MLL-PTD AML was not clear.

We aimed to (1) measure the mRNA expression levels of FLT3, BAALC, FHIT, MN1, and ERG genes in AML patients with MLL-PTD (2) compare the expression levels of these genes with normal controls, and (3) determine their prognostic significance.

Bone marrow samples from 93 de novo AML patients with MLL-PTD at diagnosis were analyzed. MLL-PTD was screened by Southern blot analysis or reverse transcriptase polymerase chain reaction (RT-PCR) then confirmed by real-time quantitative PCR (RQ-PCR). RQ-PCR assay with TaqMan probe was performed to measure the expression of FLT3, BAALC, FHIT, MN1, and ERG genes in MLL-PTD AML as well as in 34 normal controls for comparison. The expression levels of target genes were calculated as the copy number of each gene normalized to the copy number of ABL control gene (NCN). Positive and negative controls as well as standard curve constructs were included in each assay. Mutational analysis was performed by DNA/cDNA PCR followed by GeneScan analysis for detection of internal tandem duplication of FLT3 gene (FLT3/ITD). The expression levels of each target genes were dichotomized at the median value to low and high expression groups. The event-free and overall survivals (EFS and OS) were compared between the 2 groups.

The expression levels of mRNAs for FLT3, BAALC, FHIT, MN1, and ERG genes at diagnosis in MLL-PTD AML and 34 normal controls are shown in Table.

MLL-PTD patients had significantly higher expression levels of FLT3, BAALC, MN1, and ERG compared to normal controls. The expression of FHIT was also higher than that of controls, but did not reach statistic significance. FLT3/ITD was present in 26 of 52 patients (50%). The expression levels of the above genes were not different between patients with FLT3/ITD and those without. The median age of the entire cohort was 56 years. The median EFS and OS of the 52 patients who received standard induction chemotherapy were 5.8 and 11.4 months, respectively. The complete remission (CR) rate was higher in the low expression group than that of high expression group for BAALC (P = 0.011). The CR rate was not significantly different between low and high expression groups for FLT3, FHIT, MN1, or ERG, and between FLT3/ITD(+) and (-) groups. There were no significant difference in EFS or OS between patients with FLT3/ITD and those without. Patients with high expression of BAALC had a significantly shorter survival than those with low expression group; the median EFS was 10.3 mons (95% CI: 5.9-14.7 mons) vs. 0 mon, P = 0.044 and the median OS was 16.4 mons (95% CI: 8.3-25.5 mons) vs. 10.9 mons (95% CI: 6.5-15.3 mons), P = 0.031. Patients with high expression of MN1 also had a poor outcome compared with low expression group; the median EFS was 10.9 mons (95% CI: 0-28.3 mons) vs. 4.1 mons (95% CI: 0-11.7mons), P = 0.002 and the median OS was 29.7 mons (95% CI: 0-70.7mons) vs.11.0 mons (95% CI: 10.7-11.3 mons), P = 0.024. The EFS and OS were not significantly different between low and high expression groups for FLT3, BAALC, FHIT, and ERG.

Our results showed that MLL-PTD was associated with overexpression of FLT3, BAALC, MN1, and ERG. The patients with lower expression level of BAALC had a higher CR rate and patients with overexpression of BAALC or MN1 had poor EFS and OS. FLT3/ITD had no prognostic impact.

Supported by grants NSC97-2314-B-182 -011-MY3, NSC96-2314-B-195-006-MY3, and MMH-E-96009.

No relevant conflicts of interest to declare.