RB1 and acute lymphoblastic leukemia: Unlike reported in the previous study by Benard-Slagter et al. (19), which showed the presence of homozygous deletion of CD200 and heterozygous deletion of BTLA, we identified a case of ALL relapse with heterozygous deletion of CD200 and a homozygous deletion of BTLA. One case of B-ALL with iAMP21 amplification showed homozygous deletion of CD200 and BTLA and gene deletions in RB1, TP53, CTCF as has been reported earlier (24).