High BAALC Expression as an Independent Adverse Risk Factor in 309 Patients with Acute Myeloid Leukemia (AML) and Normal Cytogenetics: Results of the SHG’96 Study.
Authors: Baldus Claudia D. , Thiede Christian , Bloomfield Clara D. , Thiel Eckhard , Ehninger Gerhard 
Published: October 2019

High mRNA expression levels of the human gene BAALC (Brain And Acute Leukemia, Cytoplasmic) have been shown to be an adverse risk factor in newly diagnosed AML patients (pts; Blood2003;102:1613). The first study included 86 de novo AML pts under the age of 60 with normal cytogenetics and a more favorable FLT3 mutation status, which were uniformly treated on the Cancer And Leukemia Group B protocol 9621. An independent confirmation of these data is necessary, to confirm the impact of BAALC expression in intermediate risk AML pts. Here we present the results of a Süddeutschen Hämoblastosegruppe (SHG) study including 309 adult pts diagnosed with de novo (n=280) and secondary AML (n=29), normal cytogenetics, age <60 years that were uniformly treated on the SHG’96 protocol. Treatment consisted of 2 cycles of induction therapy followed by intensive consolidation including autologous as well as allogeneic stem cell transplantation. Median follow-up for patients alive was 28.7 months (range: 0–86 months). BAALC expression was measured in pretreatment peripheral blood blasts by comparative real-time RT-PCR. Pts having BAALC expression values within the lower 50% were classified as low BAALC and pts having BAALC expression values within the upper 50% were classified as high BAALC. Whereas no correlation was seen between BAALC expression and the prevalence of FLT3 internal tandem duplications (ITD; P=0.16), high BAALC patients had a significantly higher FLT3 mutant/wild-type (wt) ratio as determined by Genescan analysis (mean mutant/wt ratio: 0.59 vs. 0.17; P=0.012). There was no significant difference in the prevalence of MLL partial tandem duplications between the high and the low BAALC group. High BAALC expression was significantly more frequent in FAB groups M0/M1 as compared to the other subtypes (P=0.002). Pts with high BAALC expression levels had a significantly lower CR rate (62.3% vs. 73.5%; P=0.039) and a higher relapse rate (43.8% vs. 28.9%; P=0.030). The overall survival (OS) was significantly shorter for pts with high BAALC expression (OS at 4 years: 29.8% vs. 53.3%; P=0.0018), event-free survival (EFS, at 4 years: 21.6% vs. 45.8%; P=0.0001), and disease-free survival (DFS, at 4 years: 30.4% vs. 57.6%; P=0.0018). Pts with a high FLT3 mutant/wt ratio (greater than 0.8) had a significantly shorter OS and DFS. For patients with a low FLT3 mutant/wt ratio, high BAALC expression allowed identification of pts with a high risk of treatment failure. A multivariate analysis confirmed high BAALC expression and a high mutant/wt FLT3 ratio as the only independent adverse risk factors. For pts with high BAALC expression the hazard ratio of death was 1.7 (95% CI 1.18–2.48; P=0.005), and the hazard ratios for EFS and DFS were 1.8 (95% CI 1.3–2.6; P=0.0003) and 2.0 (95% CI 1.2–3.3; P=0.004), respectively. In conclusion, this independent and larger study strengthens high BAALC expression as one of the most relevant adverse prognostic risk factors in intermediate risk AML pts with normal cytogenetics. Thus, determination of BAALC expression should be considered for risk adaptive treatment strategies.