Concurrent gene mutations detected in the 48 CLL cases with SPEN mutations included the following: 21 (43.7%) NOTCH1, 11 (22.9%) TP53, 6 (12.5%) BIRC3, 5 (10.4%) SF3B1, 4 (8.3%) XPO1, 3 (6.2%) MUC2, 2 (4.2%) ATM, 2 (4.2%) FBXW7, 2 (4.2%) BTK, 1 (2.1%) POT1, 1 (2.1%) ZMYM3, 1 (2.1%) MYD88, 1 (2.1%) CXCR4, and 1 (2.1%) LRP1B (Figure 1). The gene discussed is BTK; the disease is B-cell chronic lymphocytic leukemia.