Different groups reported that malignant cells that recently interacted in vivo with the supportive microenvironment of lymphoid tissues (9, 10), or those that were cultured in vitro with different signals that mimic microenvironment stimuli (11–15), show an increased expression of BCL-XL and MCL-1 and are less sensitive to venetoclax compared to quiescent or unstimulated CLL cells. The gene discussed is BCL2L1; the disease is B-cell chronic lymphocytic leukemia.