RB1 and acute lymphoblastic leukemia: In the refined risk classification of childhood ALL, favorable genetic features include ETV6-RUNX1, hyperdiploidy, lack of deletion of IKZF1, CNKN2A/B, PAR1, BTG1, EBF1, PAX5, ETV6 or RB1, isolated deletions affecting ETV6/PAX5/BTG1, and deletions of ETV6 with an additional deletion of BTG1/PAX5/CDKN2A/B; other genetic features are classified as risk factors [48].