- The stimulation through the BCR can be blocked by ibrutinib, which is an oral drug that selectively inhibits Bruton s tyrosine kinase (BTK). In clinical trials, ibrutinib demonstrated safety and high response rates in patients with high-risk disease. Ibrutinib has gained FDA approval as a treatment for CLL regardless of prior treatment or cytogenetic status. However, single-agent ibrutinib has limitations; the drug does not eliminate all tumor cells and, with time, the tumor cells may become resistant. Therefore, combination of ibrutinib with other drugs could be beneficial.