Fixed Duration Ibrutinib/Venetoclax Feasible for Some CLL/SLL

Walter Alexander

December 08, 2020

Among chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL) patients in the minimal residual disease (MRD) cohort of the phase 2 CAPTIVATE trial, a 1-year disease-free survival (DFS) rate of 95% in those randomized to placebo after 12 cycles of combined ibrutinib plus venetoclax supports a fixed-duration treatment approach, according to William G. Wierda, MD, PhD, University of Texas, MD Anderson Cancer Center, Houston.

Ibrutinib, a once-daily Bruton kinase inhibitor, is the only targeted therapy for first-line treatment of CLL that has demonstrated significant overall survival benefit in randomized phase 3 studies, Wierda said at the American Society of Hematology annual meeting, held virtually.

Ibrutinib and venetoclax have synergistic and complementary antitumor activity, he noted, through mobilizing and clearing CLL cells from protective niches and disease compartments beyond blood and bone marrow.

Fixed-Duration Study

CAPTIVATE (PCYC-1142), an international phase 2 study, evaluated first-line treatment with 12 cycles of the ibrutinib/venetoclax combination in MRD and fixed-duration cohorts. The current primary analysis of 1-year DFS from the MRD cohort tested whether the regimen allows for treatment-free remission in the setting of confirmed undetectable MRD (uMRD).

Patients (n = 164, median age 58 years) in the CAPTIVATE study MRD cohort had previously untreated active CLL/SLL requiring treatment per International Workshop on Chronic Lymphocytic Leukemia criteria.

They received 3 cycles of lead-in ibrutinib (420 mg once daily) followed by 12 cycles of ibrutinib (420 mg once daily plus venetoclax ramp-up to 400 mg once daily). Thereafter, in an MRD-guided 1:1 randomization stratified by immunoglobulin heavy chain (IGHV) mutational status, those with confirmed uMRD received either placebo or ibrutinib, and those with uMRD not confirmed received either ibrutinib or ibrutinib plus venetoclax (both open-label).

Among high-risk features in CAPTIVATE subjects, 60% of patients had unmutated IGHV, with del(17p)/TP53 mutation in 20%, del(11Q) in 17%, complex karyotype in 19%, cytopenias in 36%, bulky lymph nodes in 32%, and absolute neutrophil count ≥25x109/L in 76%.

Response Findings

The ibrutinib lead-in, Wierda said, reduced tumor lysis syndrome (TLS) risk, shifting 90% of patients with high baseline TLS risk to medium or low-risk categories (from 77 to 51 patients), precluding need for hospitalization with venetoclax initiation.

The rate for best response of uMRD (defined as uMRD over at least 3 cycles in both peripheral blood and bone marrow) in evaluable patients was 75% in peripheral blood (n = 163) and 72% in bone marrow (n = 155).

Confirmed uMRD was achieved in 86/149 (58%), with uMRD not confirmed in 63/149 (uMRD 32% in bone marrow and 48% in peripheral blood). One-year DFS after the further randomization to placebo or ibrutinib in the confirmed uMRD group was 95.3% in the placebo group and 100% in the ibrutinib group (P = .1475). In the uMRD not confirmed group, 30-month progression-free survival (PFS) was 95.2% and 96.7% in the ibrutinib and ibrutinib plus venetoclax groups, respectively. Thirty-month PFS rates in the confirmed uMRD placebo and ibrutinib arms were 95.3% and 100%. "Thirty-month PFS rates were greater than 95% across all randomized arms," Wierda stated.

In patients without confirmed uMRD after 12 cycles of combined ibrutinib plus venetoclax, additional randomized treatment led to greater increases in uMRD in the ibrutinib plus venetoclax group than in the ibrutinib alone group (bone marrow additional 10% ibrutinib alone, 34% ibrutinib plus venetoclax; peripheral blood 0% ibrutinib, 19% ibrutinib plus venetoclax).

Adverse events generally decreased after the first 6 months of ibrutinib plus venetoclax treatment, with no new safety signals emerging over time. "There were no safety concerns with this highly active combination of first-line ibrutinib plus venetoclax. It's an oral, once-daily fixed duration regimen that achieves undetectable MRD in blood or bone marrow in three-fourths of patients after 12 cycles of combined treatment."

When asked, in a question-and-answer session after his presentation, if the findings were "practice changing," Wierda responded: "We need additional data from ongoing studies looking at various combinations of targeted therapy. But this study does clearly show efficacy in terms of depth of remission, and it supports the concept of fixed duration treatment, particularly for those patients who achieved undetectable MRD status."

SOURCE: William G. Wierda, MD, PhD. ASH 2020, Abstract 123.

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