ORLANDO – Idelalisib given as first-line therapy for patients with chronic lymphocytic leukemia carries a high risk of early fulminant hepatotoxicity requiring drug interruption and steroids, investigators reported.
Among 24 patients who received idelalisib (Zydelig) monotherapy in a phase II trial of a combination of idelalisib followed by idelalisib concurrent with ofatumumab (Arzerra) as first-line therapy for chronic lymphocytic leukemia (CLL), 12 patients developed acute hepatotoxicity, marked by rapidly soaring levels of transaminase within about 28 days of starting therapy. An additional four patients developed hepatotoxicity at around 130 days, noted Dr. Benjamin L. Lampson, a clinical fellow in medicine at the Dana-Farber Cancer Institute in Boston.
Dr. Benjamin Lampson
“Multiple lines of evidence suggest that this early hepatotoxicity is immune mediated. The proportion of regulatory T cells in the peripheral blood decrease on idelalisib therapy, providing a possible explanation for the development of early hepatotoxicity,” he said at the annual meeting of the American Society of Hematology.
The toxicities occur more frequently among younger and less heavily pretreated patients, and are likely due to on-target, immune-mediated effects, he noted.
Dr. Lampson presented data on the first 24 patients in an ongoing phase II trial. Patients with previously untreated CLL receive idelalisib 150 mg twice daily for 56 days, in an attempt to mobilize neoplastic B cells from the peripheral lymphoid tissues and into the bloodstream.
Following the monotherapy phase, patients are given ofatumumab in an attempt to clear the disease from peripheral blood.
“This dosing strategy is slightly different than what has been previously been used in trials combining these particular drugs. Specifically, previously reported trials have started these agents simultaneously without a lead-in period of monotherapy,” Dr. Lampson explained.
When the lead-in phase is completed, patients receive idelalisib plus ofatumumab infusions once weekly for 8 weeks, followed by once-monthly infusions for 4 months. Patients then continue on idelalisib indefinitely. The primary endpoint is the overall response rate assessed 2 months after the completion of the combination therapy.
For the first 24 patients treated as of Nov. 9, 2015, the median time on therapy was 7.7 months and median follow-up was 14.7 months.
The median patient age was 67.4 years (range 57.6-84.9). CLL genetics showed that 13 patients had unmutated immunoglobulin heavy chain variable region (IgHV) disease, 4 had the 17p deletion and TP53 mutation, 1 had deletion 11q, and 13 had deletion 13q; some patients had more than one mutation.
“What we began to notice after enrolling just a few subjects on the trial was that severe hepatotoxicity was occurring shortly after initiating idelalisib,” Dr. Lampson said.
He presented one case, a 58-year-old man who was in the idelalisib monotherapy phase of the study. He developed grade 3 hepatotoxicity 28 days after starting the drug, despite having a normal liver function test just 1 day earlier. The drug was stopped, but his liver function tests continued to rise, suggesting a self-perpetuating or self-sustaining process.
On day 32, the patient was admitted to the hospital, and on day 33 he was started on steroids, based on the hypothesis that the hepatotoxicity might have been immune mediated. Two days after initiation of steroids, his liver function tests continued to rise, whereupon he was started on mycophenolate mofetil.
“With these two forms of immunosuppression, the [liver function tests] did eventually normalize, although the steroids and mycophenolate had to be tapered over a period of many weeks. And this patient was not the only patient to experience toxicity; in fact, hepatotoxicity was frequent and often severe,” he said.
At the time of maximum incidence, week 4, the percentage of patients with any hepatotoxicity was 46%, with 13% at grade 4, and 21% at grade 3.
“The median time to initial development of hepatotoxicity is 28 days. This suggests that the mechanism of hepatotoxicity is not immediate, but takes time to develop, consistent with an adaptive immune response. Furthermore, hepatotoxicity is typically occurring before the first dose of ofatumumab is occurring at week 8, suggesting idelalisib alone is the cause of the hepatotoxicity,” Dr. Lampson said.
A comparison of data from the ongoing study and from three previous studies – two with idelalisib in relapsed refractory disease, and one as first-line therapy in patients 65 and older – showed that grade 3 or greater hepatotoxicity was lowest in a phase I trial of idelalisib in which patients had received a median of five prior lines of therapy, occurring in only 1.9% of patients. In contrast, in the current study, 52% of patients experienced grade 3 or 4 transaminitis at some point in the trial.