A blood cancer specialist discusses how the development of tyrosine kinase inhibitors in the 1990s to treat chronic myelogenous leukemia drove major oncology advancements over the next three decades.
While chronic myelogenous leukemia (CML) is considered a rare disease, this myeloproliferative neoplasm subtype has drastically changed the medical oncology world as a whole, explained Dr. Jeffrey R. Schriber, director of Hematologic Malignancies at the Cancer Treatment Centers of America in Phoenix.
“It’s CML that has literally changed the way that we treat every cancer,” Schriber said in an interview with CURE®, where he reflected on highlights in CML treatment over the last two decades in light of CURE®’s 20th Anniversary.
TKIs Improve CML Outcomes, Launch New Era in Cancer Medicine
Decades ago, the only hope for curing CML was for a patient to undergo an allogeneic stem cell transplant. Though curative, it had risks — including mortality, long hospital stays and becoming very ill. Then, in the late 90s, researchers figured out a way to target the specific protein that was contributing to the proliferation of the disease. Thus, a new class of drugs called tyrosine kinase inhibitors (TKIs) was born.
At first, TKIs were tested out on patients with late-stage CML that has progressed into acute myeloid leukemia, which traditionally had average prognosis of less than five years.
“When (TKIs) first came out, it was around the time when some of the Harry Potter novels were coming out. When patients were in that final stage of CML, they usually live less than a month and they were very sick,” Schriber said. “All of a sudden they try this new pill, because they tried the most extreme cases first, and it was like breathing life back into the patient. There’s a Harry Potter scene when they do that.”
Nearly all patients — over 95% of them, in fact — respond to TKI therapy, meaning that their disease shrinks as a result of treatment, Schriber explained. Now with fewer patients needing transplants, they are not only living longer, but also have improved quality of life.
Schriber also noted that some patients can stop treatment if their blood counts return to normal for long enough, while others may need to stay on therapy forever.
“But for all intents and purposes, these patients live normal lives,” he said.
The advent of TKIs not only improved the lives of patients with CML, but it was also one of the first advances in oncology that focused on specific targets rather than administering broadly toxic drugs like chemotherapy, which harm not only cancer cells, but healthy cells as well.
“This really started the field of molecular medicine, where if you identified what was wrong, then you can target it and go after that. That’s what we do now in medicine, not just in hematologic malignancies, but in all sorts of malignancies,” Schriber said.
Overcoming Resistance to TKIs
Despite the exciting improvements that TKIs have brought to the treatment of CML, it is still not a perfect method of treatment, as some patients’ diseases will grow resistant to the drugs.
“Cancer cells want to keep living. So, if we develop a therapy, they will try to develop some ways to evade it. It evolves and changes,” Schriber said, noting that sometimes CML cells will develop a T315I mutation that will make them resistant to TKI therapy.
This October, the Food and Drug Administration (FDA) approved Scemblix (asciminib) for certain patients with CML who have a T315I mutation and/or are not tolerant to, or have inadequate responses to TKIs.
Ultimately, developments like these will continue to make CML — a disease that once could be life-threatening — to something that can be managed long-term.
“So what we have to do is continue to stay ahead of the game and say how do we continue to evolve and improve things?” Schriber said.
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