Overmortality of Icsbp^−/−Nf1^+/− mice resulting from leukemias. (A) Kaplan-Meier survival curves of Icsbp^−/−Nf1^+/− (●, n = 50); Icsbp^−/−Nf1^+/+ (○, n = 56); Icsbp^+/+Nf1^+/− (▲, n = 41); and Icsbp^+/+Nf1^+/+ (△, n = 32). (B) Comparison of total leukocyte counts, spleen weight normalized to body weight, and normalized liver weights of each individual diseased mouse. Dots represent individual measurements; and lines, medians. The level of significance (Mann-Whitney U test) comparing Icsbp^−/−Nf1^+/− and Icsbp^−/−Nf1^+/+ mice is shown above dots for Icsbp^−/−Nf1^+/− (n = 26); Icsbp^−/−Nf1^+/+ (n = 9); Icsbp^+/+Nf1^+/− (n = 8); and Icsbp^+/+Nf1^+/+ (n = 2). (C) Extensive enlargements of lymph nodes, liver, and spleen of Icsbp^−/−Nf1^+/− diseased mice. (D) Disease incidences and overall distribution of leukemias in all 4 genotypes. Mice were observed until the age of 15 months. Necropsy was performed on all mice either after the observation period or in case of clinical signs of disease. Some mice that died unexpectedly without disease manifestation (ie, dead without prior disease) could not be investigated. In some mice (moribund, no leukemia) cause of death could not be established, but a hematologic disease could be excluded. *Statistically significant difference (P < .001 by χ² test) for the incidence of leukemia.