Disease progression has been increasingly appreciated with the use of ibrutinib to treat chronic lymphocytic leukemia (CLL). Understanding the pattern of clonal evolution and transcriptomic changes during the early treatment period with ibrutinib may provide insight into the mechanisms of resistance. We performed whole exome sequencing on sequential samples with matched germline controls from 61 patients with CLL during the first 12 months of ibrutinib monotherapy or ibrutinib in combination with rituximab. Additionally, RNA sequencing was done on a subset of 14 patients treated with ibrutinib monotherapy. The presence of clonal shifts was associated with an increased risk of disease progression, suggesting that resistant clones are more likely to emerge in CLL with greater evolutionary... (for more see dbGaP study page.)