Two different obinutuzumab-based chemoimmunotherapy regimens resulted in excellent long-term disease control as front-line therapy for chronic lymphocytic leukemia (CLL), investigators said in a follow-up report on a phase 1b study.
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Both obinutuzumab plus fludarabine/cyclophosphamide (G-FC) and obinutuzumab plus bendamustine (G-B) were well tolerated, with adverse events similar to what has been reported in rituximab-containing immunotherapy regimens, they said in the report of final results from the GALTON trial.
Most evaluable patients had B-cell recovery by 36 months in the study, which included a population of CLL patients largely without 17p deletions, said Jennifer R. Brown, MD, PhD, of Dana-Farber Cancer Institute, Boston, and her coinvestigators.
“These data support moving forward with these regimens in subsequent trials, which are currently ongoing,” they said in their report on the study, which appears in Blood.
The open-label, parallel-arm, multicenter phase 1b GALTON study included 41 patients with CLL, of whom 21 received G-FC and 20 received G-B for up to six cycles of 28 days each. The median age was 60 years, and about one-third of patients had Rai stage III or IV disease. Only one patient had del(17p), and nearly half of patients tested (17 of 38 patients) had unmutated immunoglobulin heavy-chain variable region gene (IGHV). Six patients had del(11q), including four in the G-FC arm and two in the G-B arm.
Both G-FC and G-B had manageable toxicities, with infusion-related reactions being the most common adverse event, occurring in 88% (20% grade 3 or 4), Dr. Brown and her colleagues reported, adding that grade 3 or 4 neutropenia was seen in 48% of the G-FC arm and 55% of the G-B arm.
The objective response rate (ORR) was 62% for G-FC and 90% for GB.
“The ORR in the G-FC arm likely does not reflect the true activity of the regimen, as it is based on an intent-to-treat analysis,” the investigators said.
With a median observation time of 40.4 months, 95% of patients were alive, and 90% had not experienced a progression-free survival event.
Nine patients in the G-FC arm underwent minimal residual disease (MRD) testing in peripheral blood; 100% had undetectable MRD, according to the report.
“With the caveat of small patient numbers and inevitable differences in patient populations across studies, these results suggest that G-FC may clear residual disease more effectively than rituximab plus FC,” the investigators wrote.
Previous studies of R-FC showed an undetectable MRD rate of 45% or less, they said.
The study was sponsored by Genentech. The investigators reported disclosures related to Genentech/Roche and other companies.
SOURCE: Brown JR et al. Blood. 2018 Dec 28. doi: 10.1182/blood-2018-06-857714.