PLCG2 and B-cell chronic lymphocytic leukemia: Woyach et al. performed exome sequencing at baseline (before start of ibrutinib treatment) and at the time of relapse on six CLL samples and identified BTKC481S mutation in 83% (5/6) patients, and PLCG2 mutation in 33% (2/6) patients, that were not in baseline samples [17].