A multi-center, international, randomized, Phase III study of older untreated patients with chronic lymphocytic leukemia (CLL) demonstrated that ibrutinib, a kinase inhibitor, is significantly more effective than traditional chemotherapy with chlorambucil.
The study, which followed 269 patients, revealed a 24-month overall survival rate of 97.8% for patients taking ibrutinib versus 85.3% for those on chlorambucil. Minor adverse effects were reported.
“Ibrutinib was superior to chlorambucil in CLL patients with no prior treatment, as measured by progression-free survival, overall survival, and response,” said Burger, an associate professor of Leukemia. “The study also revealed significant improvements in hemoglobin and platelet levels.”
Ibrutinib, marketed as IMBRUVICA®å by its developer, Pharmacyclics, an AbbVie Company, was previously FDA-approved for treating mantle cell lymphoma and CLL patients who had relapsed after prior treatments.
“CLL is the most common adult leukemia in western countries, and primarily affects older patients with a median age of 72 years at diagnosis,” said Burger. “In many countries, chlorambucil has remained the standard first-line therapy for such patients since the 1960s. This study paves the way for the use of ibrutinib in the front-line therapy setting.”
In patients with CLL, B cells continuously grow and accumulate in the lymph nodes, bone marrow and blood, where they crowd out healthy blood cells. CLL cell growth is driven by the B cell receptor (BCR), a molecule on the surface of the leukemia cells, which transmits growth signals into the cells using enzymes, including Bruton’s tyrosine kinase (BTK).
Ibrutinib attaches itself to BTK, and thereby blocks BTK function, shutting down the growth signals and consequently leading to CLL cell death. Ibrutinib also disables tissue anchor signals on the leukemia cells, removing CLL cells from the lymph nodes’ nurturing environment, causing them to starve.
Patients were randomly assigned to receive either ibrutinib or chlorambucil, both oral medications. Median age of study patients was 72 years, and 44% had advanced stage disease. The median follow-up was 18.4 months, with 87% of ibrutinib-treated patients still continuing their treatment at the time of analysis. Side effects occurred in 20 percent of patients and included diarrhea, fatigue, cough and nausea.