In the prospective cohort, at least 1 mutation classified as pathogenic or likely pathogenic was identified in 50 of 87 (57.5%) CLL, including mutations in BTK, PLCG2, or BCL2 in samples collected at relapse after treatment with BTK or BCL2 inhibitors, respectively (Supplemental Digital Content; Suppl. This evidence concerns the gene BCL2 and B-cell chronic lymphocytic leukemia.