Martin JS Dyer, MA, DPhil, FRCP, FRCPath from the University of Leicester, Leicester, UK, provides an overview of a Phase I study of ONO/GS-4059, a selective Bruton’s tyrosine kinase (BTK) inhibitor, in relapsed and refractory mature B-cell malignancies. Prof. Dyer presents the data showing the reduced toxicity of ONO/GS-4059 in comparison with the 1st generation BTK inhibitor ibrutinib.