To clarify the TP53 gene status in B-precursor ALL cell lines with representative chromosomal translocations, we analyzed 32 B-precursor ALL cell lines including 10 MLL-rearranged ALL [9], 6 t(1;19)-ALL, 7 Ph1-positive ALL [10] , and 4 t(17;19)-ALL cell lines [11] using the yeast functional assay [12] , which is sensitive for detecting TP53 mutation. TP53 mutation was detected in 13 cell lines (40.6%) ( Table I ). The incidence of TP53 mutation in the present study is higher than that in previous reports that used primary ALL samples at diagnosis, in which TP53 mutation was identified in 2% of the cases [2, 3] , suggesting that acquisition of TP53 mutation might provide advantages for disease progression and/or sustained proliferation in vitro.