Venetoclax Re-Treatment of Chronic Lymphocytic Leukemia (CLL) Patients after a Previous Venetoclax-Based Regimen

BACKGROUND:

Treatment of chronic lymphocytic leukemia (CLL) with a fixed-duration venetoclax (Ven)-based regimen is now a standard of care (SOC) option for both frontline and relapsed refractory (R/R) disease based on results of the CLL14 and MURANO trials (Fischer et al NEJM 2019, Seymour et al NEJM 2018). As fixed-duration Ven regimens are now a SOC, it is expected that an increasing number of patients (pts) will ultimately progress after Ven exposure and require additional CLL-directed therapy. While many discuss re-treatment with Ven as a subsequent treatment option, the current literature contains response data on an extremely limited number of evaluable pts (11 pts MURANO, overall response rate (ORR) 55%; 3 pts VEN 365, ORR 100%). Whether re-treatment with Ven is an acceptable option remains an important unanswered clinical question.

METHODS:

We conducted a multicenter, retrospective study of CLL pts treated with a Ven-based regimen (Ven1) and then re-treated with a second Ven-based regimen (Ven2) in a later line of therapy (LOT). Data were collected from 13 centers and the CLL Collaborative Study of Real-World Evidence database. CLL pts were eligible for inclusion if they were treated with a Ven-based regimen in any LOT and then re-treated with a Ven-based regimen as a later LOT. Collected data included demographics, prognostic disease characteristics, tumor lysis syndrome (TLS) risk and incidence, clinical response and reasons for treatment discontinuation (dc). The primary study endpoint was investigator-assessed ORR (CR: complete response, PR: partial response, SD: stable disease, PD: progression of disease, iwCLL 2018). Kaplan-Meier method was used to estimate progression free survival (PFS). All other analyses were descriptive.

RESULTS:

We identified 25 pts who were re-treated with Ven. Pt characteristics prior to treatment with Ven1 are summarized in Table 1. In 24% of pts (n=6), Ven1 was administered as part of a clinical trial. Median prior LOT was 2 (range 0-10) with 12.0% treatment naïve and 60% with prior BTKi exposure. The majority of pts had ≥1 high-risk prognostic marker: del17p (39%), TP53 mut (27%), complex karyotype ≥5 abnormalities (30%) and unmutated IGHV (84%). For Ven1, treatment regimens, TLS risk, and dose are summarized in Table 2.

With a median duration of exposure of 15 months (mos) (64% pts > 12 mos) for Ven1, the ORR was 88% (CR: 48%, PR: 40%, Figure 1A). Ten pts had minimal residual disease (MRD) assessments by flow cytometry; 8 pts (80%) achieved undetectable MRD (10^-4). Most common reasons for Ven1 dc included: toxicity (28%), completion of planned therapy (24%), MD/pt preference (24%), other (12%), alloHSCT (4%) and cost (4%).

There was a median of 8.7 mos (36% > 12 mos) between Ven1 and the initiation of Ven2, and 88% did not receive another LOT between Ven1 and Ven2. Reasons for Ven2 initiation were either CLL progression (87.5%) or MRD-positive relapse (12.5%). For Ven2, TLS risk, TLS incidence and dose information are outlined in Table 2. TLS was a rare event during Ven re-treatment (4.5%, lab only). For Ven2, Ven monotherapy was the most common regimen (52%). Standard Ven dose-escalation was used for re-initiation in 17 of 19 pts with available data, however 1 pt started Ven2 at 400 mg daily (no TLS) and another underwent a prolonged ramp-up period.

At the time of this analysis, 18 pts had available response assessments for Ven2: ORR is 72.2% (CR: 4, PR: 9, SD: 4 and PD: 1, Figure 1B). Median time from Ven2 to progression or last follow up is 8 mos (0.2-29 mos). Median PFS has not been reached. Estimated 12-month PFS is 69.1%. For pts with a CR to Ven2, median follow up time is 14.5 mos vs 7 mos for pts with PR or SD. Of 25 pts re-treated with Ven, 68% remain on Ven2 presently and 32% have discontinued Ven2, including due to CLL progression (n=4), completion of planned therapy (n=1), unrelated death (n=1), MD/pt preference (n=1).

CONCLUSIONS:

To our knowledge, this is the largest reported cohort of CLL pts re-treated with Ven after a prior Ven-based regimen. The high ORR in this pt population (median 2 prior therapies) suggests that re-treatment is a promising strategy and should be considered in treatment sequencing algorithms. Notably, pts with a CR to Ven2 had a longer median follow up than those with a PR or SD, suggesting a likelihood of deeper responses with time. Given the promising ORR, further research to prospectively validate Ven re-treatment is warranted. Updated data will be presented.