Raúl Córdoba, MD, PhD, of University Hospital Fundación Jiménez Díaz, Madrid, Spain, discusses results from a drug–drug interaction study (NCT02381080) of ibrutinib with moderate and strong cytochrome p3a (CYP3A) inhibitors. Potential drug–drug interactions are important as ibrutinib is a novel therapy for B-cell malignancies, such as chronic lymphocytic leukemia (CLL) and mantle cell lymphoma. Ibrutinib is metabolized by an enzyme in the liver, CYP3A. If the patient has another medication it can also interact with this cytochrome; therefore resulting to ibrutinib levels becoming very high and leading to toxicity. The aim of this study is to analyze the plasma levels of ibrutinib when the patient is taking it concurrently with other drugs that may interact with the cytochrome. Recorded at the 2016 American Society of Hematology (ASH) Annual Meeting, held in San Diego, CA.