Longer survival in mice with Fzr1-deficient B-ALL than in those with Fzr1-intact B-ALL is associated with increased B-ALL cell fragility induced by DNA DSBs. (A) Survival curves for mice with B-ALL originating from Fzr1-intact (n = 14 mice) or Fzr1-deficient (n = 9 mice) BM cells. The P value was determined with the log-rank test. (B) Areas of cell death (outlined with yellow dotted lines) in hematoxylin and eosin–stained sections of B-ALL–affected lymph nodes from moribund recipient mice. Scale bars, 50 µm. (C) Proportion of lymph nodes occupied by areas of cell death as determined for sections in panel B. The data are presented as the mean ± SD (n = 3 mice per group). *P = .049. (D and F) Immunohistochemical staining for pHH3 (D) and γH2A.X (F) in affected lymph nodes from mice with Fzr1-intact or Fzr1-deficient B-ALL. Scale bars, 20 µm. (E and G) Density of cells positive for pHH3 (E) or γH2A.X (G) in areas of cell death as determined for sections similar to those in panels D and F, respectively. The data are presented as mean ± SD (n = 3 mice per group). P = .191 for pHH3; *P = .0077 for γH2A.X.