Here, Lydia Scarfò, MD, of Vita-Salute San Raffaele University, Milan, Italy, gives an interesting insight about the possible reasons behind ibrutinib resistance in patients with chronic lymphocytic leukemia (CLL). Referring to two particular genetic mutations, BTK and PLC?2, Dr Scarfò, speaking at the 23rd Congress of the European Hematology Association (EHA) 2018, held in Stockholm, Sweden, discusses the prevalence of these mutations in patients who have relapsed post-ibrutinib treatment compared with those who are still responding, and outlines the need for future research to treat this subset of patients.