RB1 and acute lymphoblastic leukemia: Deletions involving the cyclin-dependent kinase inhibitor 2A/2B (CDKN2A/CDKN2B) cell cycle regulator loci are highly prevalent (>70% of T-ALL cases [8]); rarer chromosomal deletions recurrently inactivate retinoblastoma gene 1 (RB1) and cyclin-dependent kinase inhibitor 1B (CDKN1B) in some cases of T-ALL [31,34].