BTK and B-cell chronic lymphocytic leukemia: This is independent of major clinicobiological CLL characteristics, such as immunoglobulin heavy chain variable region gene (IGHV) status or the presence of recurrent chromosomal aberrations (Supplemental Figure 1, A and B; supplemental material available online with this article; https://doi.org/10.1172/JCI173770DS1), and is not related to BTK/PLCG2 mutation evolution, since these are not present in a detectable fraction of CLL cells early during therapy (also see below).