RB1 and precursor B-cell acute lymphoblastic leukemia: Although EBF1 mono-allelic deletions occur in a small fraction (4%) of total B-ALL cases, 25% of relapsed pediatric B-ALL patients carry EBF1 mutations and EBF1 deletion is strongly associated with a low relapse-free survival rate.7, 8 Tumors from high-risk leukemia patients such as those with BCR-ABL1 translocations or TP53/RB1 and JAK mutations are more likely to display EBF1 haploinsufficiency than those from low-risk patients.