Patterns of resistance to B cell–receptor pathway antagonists in chronic lymphocytic leukemia and strategies for management

Small-molecule kinase inhibitors, especially the two Food and Drug Administration-approved agents idelalisib and ibrutinib, have changed the treatment landscape for patients with relapsed or refractory chronic lymphocytic leukemia (CLL). However, with these positive changes comes the new challenge of managing patients who relapse after these agents. The number of patients who have relapsed after taking idelalisib and ibrutinib is low, but as the drugs gain wider use and patients are treated for longer, this number is likely to grow. Because these patients can be challenging to manage effectively, coordinated efforts now to determine how and why patients relapse along with optimal treatment strategies are required to better serve our patients in the future. As well, identification of mechanisms of resistance is crucial to develop rational strategies for management. Current work has identified mechanisms of resistance to ibrutinib, and resistance to idelalisib is also under active investigation. In this review, we will discuss these mechanisms of resistance, as well as current and potential strategies for the management of kinase inhibitor-resistant CLL.