Identification of a new subgroup of adult acute T-lymphoblastic leukemia (T-ALL) with a very favorable outcome using low ERG and BAALC expression

Abstract

7014 Background: High expression of the oncogenic ETS transcription factor ERG is an independent adverse prognostic factor in T-ALL and acute myeloid leukemia (AML). The gene BAALC similarly shows high expression in hematopoietic progenitors, downregulation with onset of differentiation, and prognostic significance in AML. Therefore, we assessed whether combined expression of ERG and BAALC would better predict outcome in T-ALL. Methods: ERG and BAALC mRNA expression was determined by realtime RT-PCR in pretherapy bone marrow of 152 adults with newly diagnosed T-ALL treated on German ALL protocols (05/93, 06/99). Patients (pts) were designated low (n=76) or high (n=76) ERG expressers based on median ERG expression and as low (n=111) or high (n=37) BAALC grouping the lower quartiles 1–3 vs. quartile 4. HOX11 and HOX11L2 expression was determined and immunophenotyping differentiated 3 T-ALL groups (early, thymic, mature). Results: High BAALC expression correlated with immature T-ALL with a higher frequency of early T-ALL (P<0.0001), CD34 positivity (P<0.0001), co-expression of myeloid markers (CD13 and/or CD33; P=0.03), and high ERG expression (P=0.02). Pts with high BAALC had fewer complete remissions (73% vs. 89%, P=0.03) and a higher relapse rate (67% vs. 32%, P=0.01) than low BAALC pts. Excluding 33 pts that had received stem cell transplantation (SCT), high expression of ERG (P=0.002) and of BAALC (P=0.0004) was associated with inferior relapse-free survival (RFS) and overall survival (OS, ERG: P=0.004; BAALC: P=0.0001) compared to low expression of ERG and BAALC, respectively. In contrast, pts with low expression of both ERG and BAALC had the most favorable outcome (5y-RFS: low ERG/low BAALC 81% vs. high ERG and/or high BAALC 33%, P<0.0001; 5y-OS: low ERG/low BAALC 69% vs. high ERG and/or high BAALC 26%, P=0.0001). On multivariable analysis low ERG/low BAALC expression was of independent favorable prognostic significance (RFS, HR: 0.18, P=0.0003; OS, HR: 0.3, P=0.001); the only other prognostic factor was the immunophenotype. Conclusions: Low expression of both ERG and BAALC identifies T-ALL pts with a distinctly favorable long term outcome, thus detecting pts that may not benefit from further treatment intensification including SCT. No significant financial relationships to disclose.