Patients on an extended clinical trial of the targeted therapy ibrutinib have their relapsed or resistant chronic lymphocytic leukemia stymied even as side effects decline more than two years into the study.
Susan O'Brien, M.D., professor of Leukemia presented a poster updating trial results Monday evening at the 55th American Society of Hematology (ASH) Annual Meeting and Exposition.
It was a busy day for MD Anderson investigators -- 21 faculty members conducted 25 oral presentations today in leukemia, lymphoma, stem cell transplantation and hemopathology.
Out of 140 patients in the phase II trial, 86 percent of those who were previously untreated had a partial or complete response to the oral drug while 88 percent of those with relapsed or treatment-resistant CLL also responded to ibrutinib. Progression-free survival at 30 months was 76 percent of patients.
"Among patients with relapsed or refractory CLL, it's really amazing that so many people would still be responding and on the drug well out over two years. This is a very exciting drug," says O'Brien.
Ibrutinib continues to be well-tolerated, with most patients staying on the drug until disease progression, O'Brien noted, rather than having to quit due to side effects or other complications. Ibrutinib does not cure CLL but cuts down the disease, halts progression and improves quality of life.
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"When you have a new drug, you always want to be on the lookout for late effects of treatment," O'Brien said. "We did not see any late, unknown effects after two years and, in fact, the early effects remain early and over time you don't have as many adverse events.
The most common side effect is diarrhea, which resolves over time. Starting with the phase I clinical trial, O'Brien and colleagues have been instrumental in developing ibrutinib and understanding how it works.
CLL is a malignancy of immune system B cells, white blood cells that create antibodies against infection. Ibrutinib blocks Bruton's tyrosine kinase (BTK), a vital component of B cell receptor signaling. CLL is the most common adult leukemia. The American Cancer Society estimates about 15,680 new cases will be diagnosed in 2013 and about 4,580 people will die from the disease.
The U.S. Food and Drug Administration approved the drug, known commercially as IMBRUVICA, for treatment of mantle cell lymphoma last month under its breakthrough therapy designation. A similar application for CLL by Pharmacyclics, Inc., the drug's developer, is pending at the FDA.
Clinical trials are under way at MD Anderson that combine ibrutinib with rituximab, an antibody that targets CLL cells, to improve response.
ASH Abstract 4163
MD Anderson news release