High expression of the transcription factor ERG predicts unfavorable outcome in acute T-lymphoblastic leukemia (T-ALL) in adults

Abstract

6505 Background: In adult T-ALL long-term survival remains limited to 32–46%. Transcription factors are frequently targeted by chromosomal translocations resulting in disruption of hematopoietic proliferation and differentiation. The oncogenic ETS transcription factor ERG is expressed during early T-cell development and shut off once T-cell commitment is complete. We hypothesized that due to its specific involvement in T-cell maturation and oncogenic potential, ERG might contribute to leukemogenesis. Thus we have determined the prognostic impact of ERG expression in T-ALL. Patients and Methods: ERG mRNA expression was analyzed by real-time RT-PCR in pretreatment marrow samples of 105 adults with T-ALL treated on German ALL protocols. Patients (pts) were dichotomized at ERG’s median expression into low (n=52) and high (n=53) expressers. HOX11 and HOX11L2 expression was determined by real-time RT-PCR. Immunophenotyping was performed differentiating T-ALL into 3 subtypes: pre-T (CD2-), thymic (CD1a+), and mature (sCD3+). Results: High ERG expression was associated with a higher relapse rate (45%) compared to pts with low ERG expression (20%; P=0.01). High ERG expressers compared to low ERG expressers had an inferior overall survival (OS, P=0.02; 5-year OS: high ERG 26% vs low ERG 58%) and relapse-free survival (RFS, P=0.003; 5-year RFS: high ERG 34% vs low ERG 72%). On multivariable analysis high ERG expression (P=0.005), immunophenotypic subgroups (pre-T vs mature vs thymic; overall P=0.04), HOX11L2 positivity (P=0.055) and absence of HOX11 expression (P=0.017) were independent adverse risk factors predicting RFS. Patients with high ERG expression had a hazard ratio (HR) for relapse of 3.2. Within the good prognostic subgroup of thymic T-ALL (n=57) high ERG (HR 4.1; P=0.02) and presence of HOX11L2 (HR 6.6; P=0.008) were independent adverse factors for RFS. Conclusion: High expression of the oncogene ERG is an adverse factor in adult T-ALL. Within thymic T-ALL otherwise classified as standard risk, high ERG expression identified pts that were more than four times likely to fail long-term RFS. The prognostic impact of ERG may assist treatment stratification and suggest the need of more intensive regimens for these high risk thymic T-ALL pts. No significant financial relationships to disclose.