New York – Venetoclax monotherapy is associated with high and durable objective response rates in patients with del(17p) chronic lymphocytic leukemia (CLL), according to efficacy findings from the open-label M13-982 trial.

Additionally, a safety expansion of the pivotal phase 2 study showed that treatment was well tolerated, and assessment of minimal residual disease (MRD) status in the peripheral blood and bone marrow of study participants correlated with the 24-month progression-free survival estimate of 100% for patients with complete remission/complete remission with incomplete blood count recovery (CR/CRi), Stephan Stilgenbauer, MD, of the University of Ulm, Germany, and his colleagues reported in a poster at the annual meeting of the International Workshop on Chronic Lymphocytic Leukemia.

Initial approval of venetoclax – a potent, highly selective, orally bioavailable, small-molecular inhibitor of BCL-2 – for del(17p) CLL was granted in 2016 based on an overall response rate of 79% and a complete remission rate of 7.5% in the 107 patients in M13-982, the investigators noted.

That response was maintained at 1 year in 85% of participants.

The current findings, which represent data through April 2017 for those 107 patients from the main cohort, as well as for 51 patients in the safety expansion study, show an overall response rate of 77%, with 20% CR/CRi.

The median time to first response was 1 month, and time to CR/CRi was 9.8 months, they said.

Estimates at 24 months for duration of response, progression-free survival, and overall survival were 66%, 54%, and 73%, respectively.

Additionally, objective responses were seen in four of five previously untreated patients who were enrolled in the safety expansion, and two of them had complete remissions. One patient with best response of stable disease decided to discontinue treatment but remained in follow-up with stable disease.

“All patients were alive at the time of analysis and remain progression free,” the investigators wrote.

In 18 patients who received prior B-cell receptor pathway inhibitor (BCRi) therapy, the objective response rate was 61% and the complete remission rate was 11%, with 12-month, progression-free and overall survival estimates of 50% and 54%, respectively.

Treatment-emergent adverse events of any grade occurred in 98% of patients, and led to dosing interruption in 40% and dosing adjustment in 17%. The most common adverse event was neutropenia; grade 3/4 neutropenia occurred in 40% of patients.

Neutropenia lead to a dose reduction in 8% of patients and to treatment interruption in 6% of patients; no discontinuations were reported.

Infections occurred in 81% of 158 patients, and grade 3/4 infections occurred in 23%; these infections were consistent with the underlying disease, the investigators said.

Laboratory tumor lysis syndrome (TLS) occurred in 5% of patients, but there were no episodes of clinical TLS, they said, noting that five TLS patients required dose interruptions. TLS occurred in four patients with medium risk at screening and in four with high risk. All episodes of TLS occurred during initial dosing or ramp-up, and all resolved. Affected patients were able to resume venetoclax with dose escalation to 400 mg/day.

The rate of minimal residual disease negativity was 30% in the intention-to-treat population as demonstrated by flow cytometry and confirmed by next generation sequencing (NGS) in 21 of 29 patients with an evaluable matched time point specimen. Bone marrow MRD negativity was observed in 20 patients by flow cytometry, and in 9 patients by NGS.

When looking at flow cytometry and NGS data combined, the MRD negativity rate in peripheral blood was 25% overall and 40% in evaluable patients, and the MRD negativity rate in bone marrow was 11% overall and 24% in evaluable patients.

Of those who achieved CR/CRi, 69% were MRD negative in peripheral blood by flow cytometry, with a 24-month, progression-free survival estimate of 100%, and 13 of those had confirmed MRD-negative blood by NGS, 2 had MRD-positive blood by NGS at a matched flow cytometry assessment, and 7 were not evaluated by NGS. For the remaining CR/CRi patients, who were MRD-positive by flow cytometry, the 24-month progression-free survival estimate was 86%.

Study participants in the main cohort were adults with a median age of 67 years who had relapsed/refractory CLL with an indication for treatment by iwCLL criteria, del(17p), good performance status, adequate bone marrow function, and creatinine clearance of at least 50 mg/min. They received a single test dose of 20 mg on day 1, with gradual ramp up to 400 mg over 4-5 weeks based on laboratory assessments. All were hospitalized for the first 20 mg and 50 mg venetoclax doses during ramp up.

Those in the safety expansion were treated with once-daily oral venetoclax starting at a dose of 20 mg/day for 1 week and ramped up to 400 mg by week 5. To mitigate TLS risk, uric acid–lowering agents and hydration were started at least 72 hours prior to administering the first dose. Those with high TLS risk – and some with medium risk – were hospitalized for the first 20-mg and 50-mg doses. Those with low TLS risk – and most with medium risk – received initial venetoclax dosing in an outpatient setting.

“Continued follow-up of patients in this trial will provide additional data on the durability of response with venetoclax in patients with del(17p) CLL,” the investigators wrote.

This study was supported by AbbVie and Genentech. Dr. Stilgenbauer received research funding, honoraria, and travel support from AbbVie, Amgen, Boehringer Ingelheim, Celgene, Genentech, Genzyme, Gilead, GSK, Janssen, Mundipharma, Novartis, Pharmacyclics, Hoffmann La-Roche, and Sanofi.

sworcester@frontlinemedcom.com

M13-982 trial in del(17p) CLL: High, durable response rates to venetoclax