MIAMI (July 24, 2026) – Scientists at Sylvester Comprehensive Cancer Center, part of the University of Miami Miller School of Medicine, and collaborators have uncovered a rare genetic mutation that enables some blood cancers to evade both approved Bruton tyrosine kinase (BTK) inhibitors and newer BTK degraders, a finding that could help shape the next generation of therapies for patients with chronic lymphocytic leukemia (CLL) and related malignancies.
Published in Cancer Discovery, the study, "Molecular and Structural Basis of Pan-Resistance to BTK Degraders and Inhibitors," identifies a mutation known as BTK A428D as a powerful mechanism of resistance to virtually every BTK-targeted therapy currently available or in development. The findings provide new insight into how cancers evolve under treatment pressure and why some patients eventually exhaust their targeted therapy options.
"The main finding was that a new BTK mutation, first described by us in 2022 , causes resistance in patients treated with BTK degraders," said Justin Taylor, M.D. , co-author of the study and physician-scientist at Sylvester. "The BTK A428D mutation has emerged as a resistance mechanism to these BTK degraders in clinical trials, and those in development, plus all approved BTK inhibitors."
BTK inhibitors have transformed treatment for CLL and other B-cell malignancies by blocking a protein that cancer cells depend on for growth and survival. More recently, researchers developed BTK degraders, a class of drugs designed to eliminate the BTK protein altogether and overcome resistance to earlier therapies.
Previous studies from Taylor's laboratory demonstrated that the most common mutations responsible for BTK inhibitor resistance remained susceptible to BTK degraders. The newly identified A428D mutation, however, appears to evade both approaches.
Using molecular, biochemical and structural analyses, the researchers found that the mutation dramatically alters the shape of the BTK protein, preventing drugs from attaching to their target.
"Understanding exactly how these resistance mutations emerge gives us a roadmap for identifying patients at risk and developing strategies to stay one step ahead of the disease," said Allison Cool, a researcher at Sylvester and co-first author of the study.
The researchers discovered that the A428D mutation changes the structure of the BTK protein in a way that prevents drugs from binding to it.
"The surprising part was that the BTK A428D has a completely different conformation that makes it impossible for any drugs to bind to it," Taylor said.
The discovery helps explain how a single mutation can drive resistance across multiple classes of BTK-targeted therapies. At the same time, the researchers found that the mutation comes with a biological tradeoff-–it reduces the fitness of cancer cells. That finding may explain why A428D is seen primarily in patients treated with BTK degraders rather than in patients receiving BTK inhibitors alone.
"The significance of this finding is that patients who develop these resistance mutations do not have any options for further BTK-targeted therapy," Taylor said.
As targeted therapies continue to improve outcomes and extend survival for patients with blood cancers, understanding how resistance develops has become one of the most pressing challenges in cancer research. By identifying the structural basis of resistance, the study provides a roadmap for developing future therapies capable of overcoming or bypassing these mutations.
The study also offers encouraging evidence that resistance may be preventable. Researchers found that combining BTK degraders with a different class of drugs that target the BCL2 protein prevented resistant cancer cells from emerging in preclinical models. The findings support further investigation of combination therapies for patients with CLL and other B-cell malignancies.
"As part of the paper, we showed that adding a different class of drug targeting the BCL2 protein to the BTK degraders can prevent the emergence of resistance," Taylor said. "Our future directions will be to further test combination therapy for CLL."
"While the A428D mutation explains resistance in some patients, our work is focused on uncovering the additional mechanisms that drive BTK degrader resistance and identifying new therapeutic approaches to overcome them," Cool said.
The research team is continuing to investigate other causes of BTK degrader resistance, as not all patients whose cancers progressed carried the A428D mutation. Scientists are also exploring new BTK-targeting strategies designed to overcome resistance and extend the benefits of precision medicine for patients with blood cancers.
The findings underscore the importance of integrating structural biology, genomics and translational research to stay ahead of cancer evolution and develop more durable cancer therapies. As researchers continue to unravel the mechanisms behind treatment resistance, the work may help pave the way for new approaches that keep patients responding to targeted therapies longer.
