In keeping with previous work highlighting that cases from the TAL/LMO gene expression subgroup tend to have a higher incidence of PTEN mutations and a lower incidence of NOTCH1 mutations [24], within our cohort of 20 patients (combining PTEN inactivation due to exon 7 mutation or copy number loss) we detected a frequency of PTEN inactivation of at least 40% (around double the frequency of PTEN inactivation (22%) detected in a recent study of 145 T-ALL cases using heteroduplex analysis, mutations and SNP arrays) [25]. This evidence concerns the gene PTEN and acute lymphoblastic leukemia.