A total of 37/54 (69%) assessed patients had BTK/PLCG2 mutations identified (19 BTK mutation only; 9 PLCG2 mutation only; 9 both BTK and PLCG2 mutations); 34/45 (76%) in patients with CLL progression and 3/9 (33%) in patients who experienced Richter transformation. The gene discussed is BTK; the disease is B-cell chronic lymphocytic leukemia.