The relationship between in vitro tipifarnib sensitivity and RAS mutational status in pediatric untreated AML and ALL samples. In vitro tipifarnib test results are depicted in LC₅₀ values (μg/mL), the concentration of tipifarnib needed to kill 50% of the cells. Each symbol represents the LC₅₀ value of an individual sample; the horizontal line depicts the median LC50 values. RAS mutational status is stated as either absence (wild-type RAS) or presence (RAS mutated). RAS mutated samples comprise mutations in either NRAS or KRAS, which are also depicted separately. (A) There were no differences in in vitro tipifarnib sensitivity between pediatric AML patients with and without RAS mutations (P = .20). In addition, there was no difference in sensitivity to tipifarnib between NRAS and KRAS mutated AML samples (P = .24). (B) There was no difference in in vitro tipifarnib sensitivity between RAS mutated ALL samples and wild-type RAS ALL samples. There were only 2 patients in both the NRAS and KRAS mutated subgroups.