A drug used to treat Waldenstrom macroglobulinemia (a type of non-Hodgkin lymphoma). It is also used to treat mantle cell lymphoma and chronic lymphocytic leukemia (CLL) in patients who have already received other treatment. It is also being studied in the treatment of other types of cancer. Ibrutinib blocks a protein called Bruton’s tyrosine kinase (BTK), which may help keep cancer cells from growing. It is a type of tyrosine kinase inhibitor. Also called Imbruvica.