Chronic lymphocytic leukemia (CLL) patients who stopped taking the kinase inhibitors (KIs), ibrutinib or idelalisib, had mostly favorable outcomes when they switched to the alternate therapy, according to a large multi-center study, conducted in part at the Perelman School of Medicine at the University of Pennsylvania.

The results will be presented by Anthony Mato, MD, MSCE, an assistant professor of Hematology/Oncology and the and director of the Center for Chronic Lymphocytic Leukemia in the Abramson Cancer Center, at the 57th annual meeting of the American Society of Hematology (Abstract 719).

While clinical studies have well documented the impressive efficacy of ibrutinib and idelalisib, two drugs approved by the U.S. Food and Drug Administration over the past year, little is known about the nearly 30 percent of patients who do not respond to those treatments, particularly outside the context of clinical research.

What alternate therapies are patients prescribed when they discontinue ibrutinib or idelalisib? Why do patients have to discontinue the drugs? Is the alternate KI effective? What are their outcomes? These are some of the key questions the team aimed to answer.

"Ibrutinib and idelalisib represent a paradigm shift in management of CLL," Mato said. "But there's a lack of data--real world practice patterns, that is - for the patients who discontinue these drugs. This is information that may eventually help guide physicians who have patients in similar scenarios. What's the best avenue to treat these patients who fail on one of these therapies? These are the types of questions we wanted to learn more about."

The researchers performed a retrospective analysis of 178 CLL patients from 10 centers across the United States. It revealed that a majority of the patients discontinued ibrutinib or idelalisib because of side effects or because their cancer progressed while taking the drugs, not Richter's Transformation, a rare complication of CLL characterized by the sudden transformation of the disease into a significantly more aggressive form of large cell lymphoma.

Patients who discontinued ibrutinib or idelalisib and went on to be treated with the other KI had durable responses, the researchers report. The objective response rate was 50 percent and median progression free survival was 11.9 months. Responses were most durable for patients who discontinued ibrutinib or idelalisib because they experienced side effects that made it difficult for them to continue taking the drug.

A clinical trial targeting this so-called "KI intolerant" patient population will be undertaken to validate these findings prospectively, the authors said.