Improving Treatment Options for Patients with Double Refractory CLL

The proliferation and survival of chronic lymphocytic leukemia (CLL) cells are heavily dependent on B-cell receptor (BCR) signaling and resistance to apoptosis. Approvals of multiple covalent Bruton's tyrosine kinas inhibitors (cBTKis) as well as the B-cell lymphoma-2 inhibitor (BCL2i) venetoclax targeting these pathways have revolutionized the treatment of CLL and small lymphocytic lymphoma (SLL). The superiority of these treatments over chemoimmunotherapy has been proven in phase III studies in both treatment-naïve and relapsed refractory settings, leading to the majority of patients with CLL being treated sequentially with cBTKis and the BCL2i venetoclax as their first- and second-line therapies. While most patients with CLL respond for many years to these sequenced treatments, they are unfortunately not curative. There remains an unmet need for effective treatment options for patients who progressed after treatment with both cBTKis and BCL2i, also referred to as double refractory patients. Treatment options for double refractory CLL has improved recently with the approval of the non-covalent BTK inhibitor (ncBTKi) pirtobrutinib as well as the CD19 targeted chimeric antigen receptor T-cell (CAR T-cell) therapy lisocabtagene maraleucel (liso-cel). These recently approved treatment options for patients with CLL with at least two prior lines of therapy have fortunately demonstrated efficacy for double refractory CLL. Additionally, there are several novel treatment options in clinical development, including bi-specific antibodies, second-generation BCL2is, new ncBTKis, and BTK degraders. Understanding resistance mechanisms to existing cBTKis and venetoclax can potentially inform us of the best utilization of available treatment options for double refractory CLL and provide a personalized approach for these patients. In this review, a challenging example of a double refractory patient with CLL will serve as the basis for a review of available literature on the treatment of double refractory CLL/SLL.