MCL1 and Richter syndrome: Interestingly, all studies that investigated combined BCL-2 and PI3K inhibition related a major part of the synergistic activity to the diminished expression levels of the anti-apoptotic proteins MCL-1 or BCL-xL irrespective of the hematological neoplasm (DLBCL, Richter’s syndrome, NHL, and AML) [18,19,20,28].