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Updated results of a phase 2 trial suggest the Bruton’s tyrosine kinase inhibitor ibrutinib can control Waldenstrom’s macroglobulinemia (WM) long-term.
In previously treated WM patients, ibrutinib produced an overall response rate of 91%.
The 2-year overall survival rate was 95%, and 69% of patients had not progressed at 2 years.
Researchers reported these results in NEJM. The research was supported by Pharmacyclics, Janssen Pharmaceuticals, and several foundations.
An earlier analysis of data from this trial supported the US Food and Drug Administration’s approval of ibrutinib as the first treatment for WM.
“These findings herald a new era for the treatment of Waldenstrom’s macroglobulinemia and show how genome sequencing can lead to the discovery of cancer mutations that can be specifically targeted by new therapies,” said study author Steven Treon, MD, PhD, of the Dana-Farber Cancer Institute in Boston, Massachusetts.
Dr Treon and his colleagues enrolled 63 WM patients on this trial. The patients had received a median of 2 prior therapies (range, 1-9), 56 patients (89%) had the MYD88L265P mutation, and 21 (34%) had the CXCR4WHIM mutation.
Patients received ibrutinib at 420 mg once daily until disease progression or unacceptable toxicity. After a median treatment duration of 19.1 months (range, 0.5-29.7 months), the overall response rate was 91%. The median time to response was 4 weeks.
Investigator-determined responses were impacted by the MYD88 and CXCR4 mutations. Patients carrying MYD88L265P and CXCR4WT achieved the highest responses, with a 100% overall response rate and 91% major response rate.
For all patients, the estimated progression-free and overall survival rates at 24 months were 69% and 95%, respectively.
“The results are remarkable when you consider that patients had received an average of 2 prior therapies, and 40% showed no response to the previous treatments,” Dr Treon said. “The findings herald a new era for the treatment of Waldenstrom’s macroglobulinemia.”
Dr Treon and his colleagues also said ibrutinib was well-tolerated. At the time of analysis, 68% of patients remained on therapy.
The most common grade 2-4 adverse events were neutropenia (22%) and thrombocytopenia (14%). Grade 3 or higher neutropenia and thrombocytopenia occurred in 9 (14%) and 8 (13%) patients, respectively.
Ibrutinib-related neutropenia and thrombocytopenia were reversible but required a dose reduction in 3 patients and treatment discontinuation in 4 patients.
Grade 2 or higher bleeding events occurred in 4 patients, and there were 15 infections considered possibly related to ibrutinib.
Treatment-related atrial fibrillation (AFib) occurred in 3 patients, all of whom had a prior history of paroxysmal AFib. AFib resolved when treatment was withheld, and all 3 patients were able to continue on therapy per protocol without an additional event.
