In two of four relapse cases, we identified previously undescribed mutations in PLCG2. Patient B06 experienced CLL relapse 12 months following combined ibrutinib and rituximab, with a rise to dominance of a subclone harboring del(8p), which we previously linked to ibrutinib resistance16. This evidence concerns the gene PLCG2 and B-cell chronic lymphocytic leukemia.