Among 13 cell lines with TP53 mutation, three cell lines had two types of mutations simultaneously; one cell line (KOPN36) had double mutation on the same allele, while two cell lines (KOPB26 and KOPN63) had two mutations on different alleles (Table I ). The distribution of the 16 mutations identified in 13 cell lines is shown in Fig. 1A and compared with that in previous reports on B-precursor ALL samples [2] [3] [4] [5] [6] [7] and T-ALL samples [18, 19] . Five (38.5%) of the 13 cell lines with TP53 mutation had missense mutation of c.743 G>A resulting in p.R248Q, and 2 cell lines (15.4%) had missense mutation of c.817C>T resulting in p.R273C; both are well known as hotspots. Among the 16 mutations, 11 mutations were located in highly con-served regions. This pattern of distribution was similar to that in B-precursor ALL samples previously reported, in which 5 (18.5%) of the 27 samples with TP53 mutation had R248Q. In contrast, R248Q mutation was reported in only one of 22 samples of T-cell ALL with TP53 mutation.