RAC2 suppression by ibrutinib is correlated with slower tumor growth in a xenograft mouse model. (A) Ibrutinib treatment resulted in growth inhibition of Mino xenografts. Tumor-bearing animals were administered 50 mg/kg ibrutinib orally (n = 6) or vehicle consisting of 0.5% methylcellulose (n = 6). Error bar represents mean ± SEM of 6 mice. The dose of 50 mg/kg was selected according to the pharmacology review of ibrutinib published by the FDA Center for Drug Evaluation and Research (accessible at https://www.accessdata.fda.gov/drugsatfda_docs/nda/2013/205552Orig1s000PharmR.pdf). (B) Immunostaining of RAC2 of Mino xenografts treated with vehicle (left) or ibrutinib (right). High-power views show cytoplasmic staining of RAC2 in individual cells. (C) RAC2 staining in 6 xenografts from either vehicle or ibrutinib group analyzed by using an unpaired Student t test. *P < .05; **P < .01.