Moreover, deletions in retinoblastoma 1 (RB1, locus on 13q14), a regulator of cell cycle progression, are found in 15% of T-ALL, and deletions involving the CDKN1B locus (12p13, encoding p27KIP1) are present in about 12% loci (32). Here, RB1 is linked to acute lymphoblastic leukemia.