Concurrent Retinoblastoma 1 ( RB1 ) and IKZF1 Deletions Have Adverse Outcome in Childhood B‐Cell Acute Lymphoblastic Leukemia (B‐ALL)

INTRODUCTION: The B-ALL risk-stratification needs improvement. The prevalence and impact of Retinoblastoma 1, that is, RB transcriptional corepressor 1 (RB1) deletion in pediatric B-ALL, alone and in concurrence with IKAROS family zinc finger 1 (IKZF1) deletion was estimated. METHODS: Multiplex ligation-dependent probe amplification (MLPA) was used to analyze the pediatric B-ALL cases for gene deletions. The cases were divided into subgroups based on RB1 deletions and IKZF1 deletions. IKZF1plus profile (IKZF1 and additional CDKN2A/B, PAX5, pseudoautosomal region deletion in absence of ERG deletion) was also noted. RESULTS: In 517 patients with median age 7 years (1-18), 41 (7.9%) had RB1 deletion and 99 (19.1%) IKZF1 deletion. Concurrent RB1 and IKZF1 deletions were 14 (2.7%), RB1 deletion without IKZF1 deletion 27 (5.2%), IKZF1 deletion without RB1 deletion 85 (16.4%), and none of RB1 or IKZF1 deletion 391 (75.6%). Of the treated patients (n = 465), cases with concurrent RB1 and IKZF1 deletions had the worst post-induction remission rate (54.6%; p = 0.019) compared to cases lacking RB1 or IKZF1 deletions (86%). The median event-free and overall survival were poor in cases with concurrent RB1 and IKZF1 deletions (8.9 months; p = 0.0002 and 11.5 months; p = 0.007 respectively) compared to cases lacking RB1 or IKZF1 deletions (41.4 months, and not reached respectively). The cases with RB1 deletion along with IKZF1plus profile had a trend of early deaths and relapses compared to IKZF1plus alone. CONCLUSIONS: The B-ALL patients with concurrent RB1 and IKZF1 deletions had worse outcomes compared to cases without any of these deletions. The RB1 deletion increased the risk of early events in patients with the IKZF1plus profile.