Given that the p53 mutational status of de novo CLL patients is often unknown, this finding indicates that ibrutinib may represent an excellent frontline treatment strategy for many CLL patients as: (1) it does not require a fully functional p53 pathway to be efficacious, and (2) this treatment does not appear to select for p53-mutant subpopulations when compared with vehicle treatment. The gene discussed is TP53; the disease is B-cell chronic lymphocytic leukemia.