Molecular Monitoring of ERG and BAALC as Minimal Residual Disease Markers in Patients with Acute Leukemia.

Although expression of the genes ERG (ETS-related gene) and BAALC (brain and acute leukemia, cytoplasmic) predicts outcome in acute leukemia, there is little information about their utility as markers of minimal residual disease (MRD). A real-time quantitative reverse transcriptase-polymerase chain reaction (RQ-PCR) was used to examine relative levels of ERG and BAALC gene expression in 11 patients with acute leukemia. Pretreatment and post-chemotherapy bone marrow (BM) samples were analyzed to quantify these transcripts. Peripheral blood (PB) samples were also obtained to evaluate the correlation of ERG and BAALC expression levels in BM and PB samples. Significant levels of ERG gene were expressed in all patients. In contrast with ERG, the levels of BAALC gene expression were significantly lower in some patients. Continuous monitoring of the ERG mRNA was performed and assessed a correlation between MRD levels and subsequent clinical courses. In patients with relative high expression of BAALC transcripts (>7x10exp-3/GAPDH), high levels of ERG gene expressions were consistently observed whether they were in remission status or not. In 2 patients with acute promyelocytic leukemia (APL), MRD was simultaneously monitored by RQ-PCR using primers for PML/RAR alpha. Changes in expression levels of PML/RAR alpha and ERG presented poor correlation. While, in other patients with relative low expression of BAALC transcripts (<7x10exp-3/GAPDH), ERG gene expression levels gradually decreased after the induction therapy and following consolidation treatments. In patients unable to attain remission, ERG expression levels remained high. Thus, the quantitation of the ERG gene expression made it possible to assess MRD in patients with acute leukemia (except for APL) carrying low BAALC expression. To our knowledge, this is the first report concerning the use of ERG mRNA expression for MRD monitoring.