When Maria first started her BTK inhibitor treatment for chronic lymphocytic leukemia, her doctors were hopeful. The drugs were working. But two years later, her cancer began growing again. She had developed a rare mutation that made her cells invisible to every BTK-targeted therapy available.
Her story illustrates a growing challenge in cancer medicine—one that scientists at Sylvester Comprehensive Cancer Center in Miami are working to solve.
Researchers at Sylvester, part of the University of Miami Miller School of Medicine, have identified a genetic mutation called BTK A428D that helps some blood cancers resist nearly every BTK-targeted treatment, including both older inhibitors and newer drugs called degraders. The findings were published in the journal Cancer Discovery.
"The BTK A428D has a completely different conformation that makes it impossible for any drugs to bind to it," said Justin Taylor, MD, a physician-scientist at Sylvester and coauthor of the study.
BTK inhibitors have transformed treatment for chronic lymphocytic leukemia, or CLL, and other B-cell cancers by blocking a protein the cancer cells need to grow and survive. BTK degraders work differently—they eliminate that protein entirely. Scientists had hoped degraders would overcome resistance to inhibitors. But the A428D mutation thwarts both approaches.
The researchers discovered that this mutation changes the shape of the BTK protein so dramatically that drugs simply cannot attach to it. This explains why a single genetic change can knock out multiple classes of therapy at once.
However, the discovery brings some good news. The mutation comes with a trade-off: it weakens the cancer cells themselves. That weakness may be the key to defeating it.
In laboratory studies, researchers found that combining BTK degraders with drugs that target a different protein called BCL2 prevented resistant cancer cells from emerging. This suggests that combination therapy could stop resistance before it starts.
"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.
Taylor noted that patients who develop these mutations currently have no further BTK-targeted options. But by understanding the structural basis of resistance, his team has given drug developers a clear target to aim for.
The hope is that future therapies might either bypass the A428D mutation entirely or combine with other drugs to prevent it from appearing in the first place. For patients like Maria, that could mean more time with their cancers controlled—and more treatment options when resistance does occur.