Bruton's Tyrosine Kinase (BTK) Mutations in Chronic Lymphocytic Leukemia (CLL): A Clinical View.

Bruton's tyrosine kinase inhibitors (BTKis) have reshaped the management of chronic lymphocytic leukemia (CLL). The first-generation BTKi ibrutinib demonstrated significant efficacy, leading to the development of second-generation agents (acalabrutinib, zanubrutinib) with improved selectivity and safety. However, resistance-most often driven by BTK mutations at the cysteine residue at position 481 (C481S)-remains a major therapeutic limitation. Noncovalent BTKis, such as pirtobrutinib, offer effective options for patients relapsing after covalent BTKi therapy. However, the emergence of novel resistance mutations continues to limit durable responses. As insights into the molecular basis of BTK resistance evolve, routine mutation testing is poised to become integral to personalized treatment in CLL. Future clinical trials are expected to adopt mutation-driven stratification to guide therapeutic sequencing. Ultimately, overcoming BTKi resistance will require innovative strategies, including BTK degraders, bispecific antibodies, and T cell-engaging immunotherapies.