The combination of venetoclax and obinutuzumab provided high response rates and deep remissions regardless of cytogenetic risk factors in patients with chronic lymphocytic leukemia, according to recently reported results of a phase 1b study.
The regimen elicited high rates of undetectable minimal residual disease in peripheral blood and had an acceptable safety profile with manageable toxicities in the study reported in Blood, which included patients with previously untreated or relapsed/refractory chronic lymphocytic leukemia (CLL).
“The deep remission rates we observed with venetoclax-obinutuzumab have not been reported with previously available CLL treatments, including FCR [fludarabine, cyclophosphamide, and rituximab], which is currently considered the most efficacious regimen with limited-duration therapy,” wrote the investigators, led by Ian W. Flinn, MD, PhD, of Sarah Cannon Research Institute/Tennessee Oncology, Nashville.
Venetoclax-obinutuzumab combinations are meanwhile being tested in other studies – including the phase 3 CLL13 and CLL14 studies – which have enrolled previously untreated fit or unfit CLL patients, respectively.
“If the primary endpoints of these large-scale trials are met, venetoclax-obinutuzumab may become a new standard treatment option in [first-line] CLL, irrespective of clinical fitness,” Dr. Flinn and his colleagues wrote in their report.
The present phase 1b, dose-escalation study enrolled 32 patients who were previously untreated (median age, 63 years) and 46 patients who were relapsed or refractory to previous treatments (median age, 61 years).
Doses of venetoclax were escalated from 100 mg to 400 mg to determine its maximum tolerated dose when combined with obinutuzumab, the investigators wrote. Some patients received venetoclax first, while others received obinutuzumab first, for a total of 1 year of treatment.
The study confirmed favorable risk-benefit treatment used a dose of 400 mg venetoclax plus the standard dose of obinutuzumab, according to the researchers.
The overall best response rate was 95% for relapsed/refractory patients, including a 37% rate of complete response or complete response with incomplete marrow recovery. In previously untreated patients, the overall best response rate was 100%, including a 78% rate of complete responses by those criteria.
Undetectable minimal residual disease was observed in 64% of relapsed/refractory patients and 91% of previously untreated patients at 3 months after the last obinutuzumab dose, the investigators reported.
There were no dose-limiting toxicities in the study, no clinical tumor lysis syndrome, and no differences between the two schedules (venetoclax first or obinutuzumab first) in terms of adverse events, the investigators wrote.
Neutropenia was the most common serious (grade 3-4) adverse event, occurring in 58% of relapsed/refractory patients and 53% of patients treated in the first line. Grade 3-4 infections were seen in 29% and 13% of the relapsed/refractory and previously untreated patients, respectively.
There were no fatal infections among previously untreated patients, while three relapsed/refractory patients (7%) had fatal adverse events, including one case of acute respiratory failure in a patient with suspected Richter’s transformation, pneumonia in a patient with metastatic squamous cell lung carcinoma, and another case of pneumonia occurring about 3 months after the last dose of venetoclax.
Genentech and AbbVie provided financial support for the study. Dr. Flinn reported receiving research funding for his institution from Genentech, AbbVie, and several other companies.
SOURCE: Flinn IW et al. Blood. 2019 Mar 12. doi: 10.1182/blood-2019-01-896290.