Treatment Sequencing in Chronic Lymphocytic Leukemia in 2024: Where We Are and Where We Are Headed

As treatments with BTK inhibitors and BCL2 inhibitors have replaced the use of chemoimmunotherapy in CLL in both first-line and relapsed patients, it becomes critical to rationalize their use and exploit the full potential of each drug. Despite their proven, robust, and manifest efficacy, BTKis and BCL2is fail to provide long-term disease control in some categories of patients, and to date this is an unmet clinical need that is critical to recognize and address. Ongoing clinical trials are evaluating new treatment algorithms and new molecules to progressively thin this population. In this review for each category of patients we explicate the different possible patterns of treatment sequencing based on currently available evidence, starting from the frontline to currently ongoing trials, in order to optimize therapies as much as possible.

Frontline Therapy of CLL-Changing Treatment Paradigms

PURPOSE OF REVIEW

The therapeutic landscape for chronic lymphocytic leukemia (CLL) has undergone a complete makeover following the introduction of highly effective targeted therapies, beginning with ibrutinib which first attained regulatory approval for CLL in 2014.

RECENT FINDINGS

In recent years, we have seen further refinement of therapeutic options with the development of newer-generation Bruton's tyrosine kinase inhibitors (BTKi) including acalabrutinib and zanubrutinib that improve upon the safety of ibrutinib. Additionally, venetoclax-based approaches, combined with anti-CD20 antibodies, have allowed for time-limited targeted therapeutic strategies which are particularly attractive for certain subsets of patients though have demonstrated efficacy across all subgroups. Lastly, there is an ongoing movement toward the development of time-limited strategies inclusive of both a BTKi and venetoclax that may further widen potential options. CLL patients requiring frontline therapy have a unique burden of choice between highly effective therapies that differ substantially with respect to side effect profiles and schedules. This review will focus on the frontline management of CLL in the setting of these rapidly changing options.

Impact of targeted agents on survival of chronic lymphocytic leukemia patients age >65 relative to age- and sex-matched population

Pooled analysis of six mature phase 3 trials (RESONATE2, ILLUMINATE, ALLIANCE041202, ELEVATE-TN, CLL14, and GLOW) evaluating Bruton's tyrosine kinase inhibitors (BTKis) and venetoclax-based treatments suggests that these agents have reduced but not completely eliminated the overall survival (OS) gap between elderly chronic lymphocytic leukemia (CLL) patients and the age and sex-matched general population (AGMGP).

Dual-targeted regimens for the frontline treatment of CLL

The treatment landscape of chronic lymphocytic leukemia (CLL) has evolved considerably over the past decade due to the development of effective novel agents with varying mechanisms of action, including Bruton tyrosine kinase (BTK) and B-cell lymphoma 2 (BCL2) inhibitors. Extrapolating upon the success of anti-CD20-directed chemoimmunotherapy, a dual-targeted approach has been explored in treatment-naive patients with CLL. Anti-CD20 monoclonal antibody combinations with BTK inhibitors as well as BCL2 inhibitors have demonstrated superiority over traditional cytotoxic chemoimmunotherapy regimens such as fludarabine, cyclophosphamide, and rituximab; bendamustine-rituximab; and obinutuzumab-chlorambucil. Impressive clinical benefit is seen in both younger and older patients, those with comorbidities, and, most importantly, those with poor prognostic features. Given this success, combinations of BTK inhibitors and venetoclax have been explored in clinical trials. These dual-targeted regimens provide remarkable efficacy while allowing for an all-oral approach and fixed duration of treatment. Current investigations under way are evaluating the utility of a triplet approach with the addition of obinutuzumab in comparison to a doublet approach.

Measurable Residual Disease Monitoring in Lymphoma

PURPOSE OF REVIEW

The utility of analyzing circulating tumor DNA (ctDNA), circulating tumor cells (CTCs), and disease in the bone marrow as an adjunctive tool in caring for hematologic cancer patients is expanding. This holds true for lymphoma where these biomarkers are being explored as a means of genotyping and quantifying disease. Regarding the latter, they can be used to monitor measurable residual disease (MRD) during and after treatment. This holds potential for aiding clinical decisions amidst treatment, detecting earlier relapse, and improving prognostication. Here, we review the evidence to support these applications in a variety of lymphoma subtypes.

RECENT FINDINGS

Numerous clinical trials across a variety of lymphomas have demonstrated value in MRD monitoring. MRD monitoring is often prognostic for progression free survival (PFS) and even overall survival (OS) at several time points in a disease course, particularly when utilizing serial measurements. With regards to tailoring treatment, there are a growing number of trials examining MRD-adaptive treatment strategies to intensify or de-escalate treatment to individualize care. Lastly, MRD monitoring has been utilized successfully in detecting earlier relapse when compared to more standard methods of clinical surveillance such as radiographic assessment. Although not routinely implemented into clinical practice, MRD monitoring in lymphoma is helping shape the future landscape of this disease by aiding in prognostication, guiding therapy, and detecting earlier relapse. Steps to standardize and further examine this technology prospectively are being taken to bring MRD monitoring to the forefront of the field.

Diagnosis and Management of Cardiovascular Effects of Bruton's Tyrosine Kinase Inhibitors

PURPOSE OF REVIEW

Bruton's tyrosine kinase inhibitors (BTKis) have changed the treatment and prognosis of several B-cell malignancies. However, since the approval of the first BTKi, ibrutinib, reports of cardiovascular adverse events especially atrial fibrillation have arisen. In this review, we discuss the cardiovascular side effects of BTKis and the management of these toxicities in clinical practice.

RECENT FINDINGS

BTKIs increase the risks of atrial fibrillation, bleeding, hypertension, heart failure, and potentially ventricular arrhythmia. Newer second and third-generation BTKis appear to have a lower risk of cardiovascular adverse events; however, long-term follow-up data are not available for these new BTKis. BTKis are an effective treatment for some B-cell malignancies; however, they can cause cardiovascular side effects. The best preventive strategies to minimize cardiovascular complications remain undefined. Currently, a practical approach for managing patients receiving BTKis includes the management of cardiovascular risk factors and side effects of BTKis to prevent interruption of cancer treatment.

Real-World Comparison of First-Line Treatment Adherence Between Single-Agent Ibrutinib and Acalabrutinib in Patients with Chronic Lymphocytic Leukemia

Purpose

Increased dosing frequency adversely affects treatment adherence and outcomes in chronic diseases; however, such data related to treatment adherence is lacking in chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL). This study compared adherence between patients treated with ibrutinib (once-daily) versus acalabrutinib (twice-daily) as first-line (1L) therapy for CLL/SLL.

Patients and Methods

Specialty pharmacy electronic medical records were used to identify adults with CLL/SLL initiating 1L ibrutinib or acalabrutinib between 01/01/2018 and 11/30/2020. Adherence was measured by the proportion of days covered (PDC) and medication possession ratio (MPR) and was compared between cohorts using odds ratios (ORs) obtained from logistic regression models adjusted for baseline characteristics.

Results

Between 01/01/2018 and 11/30/2020, 1374 and 140 patients initiated ibrutinib and acalabrutinib, respectively. Based on PDC/MPR ≥80%, patients treated with once-daily ibrutinib were more likely to be adherent than those treated with twice-daily acalabrutinib (OR ranges: PDC: 1.04-1.76; MPR: 1.03-1.58). At 6 months, patients on ibrutinib had a 58-76% higher likelihood of staying adherent compared to patients on acalabrutinib (PDC: 75.9% for ibrutinib vs 63.6% for acalabrutinib, OR: 1.76, P=0.008; MPR: 76.8% vs 66.9%, OR: 1.58, P=0.036) with a similar trend noted for the entire line of treatment (LOT) (PDC: 53.0% vs 41.4%, OR: 1.53, P=0.021; MPR: 58.7% vs 47.1%, OR: 1.50, P=0.027).

Conclusion

In this real-world analysis, CLL/SLL patients initiating 1L once-daily ibrutinib had >50% higher treatment adherence than those initiating twice-daily acalabrutinib during their LOT. Given the importance of sustained adherence for disease control in CLL/SLL, dosing frequency may be an important consideration for patients and physicians.

Unresolved questions in selection of therapies for treatment-naïve chronic lymphocytic leukemia

BACKGROUND

The treatment landscape for chronic lymphocytic leukemia (CLL) continues to undergo considerable evolution. Optimal selection of initial therapy from multiple effective options provides a major challenge for clinicians, who need to consider both disease and patient factors in conjunction with a view to sequencing available therapies in event of disease relapse.

REVIEW

We explore the most topical clinically relevant unresolved questions through discussion of important available pertinent literature and propose expert opinion based on these data. (1) Shrinking role of chemoimmunotherapy (CIT); while novel therapies are generally superior, we highlight the utility of FCR for IGHV-mutated CLL. (2) Choosing between inhibitors of Bruton's tyrosine kinase (BTKi); while efficacy between agents is likely similar there are important differences in toxicity profiles, including the incidence of cardiac arrhythmia and hypertension. (3) BTKi with or without anti-CD20 monoclonal antibodies (mAb); while obinutuzumab-acalabrutinib (AO) may confer superior progression-free survival to acalabrutinib (Acala), this is not true of rituximab (Ritux) to ibrutinib (Ib)-we highlight that potential for increased side effects should be carefully considered. (4) Continuous BTKi versus time-limited venetoclax-obinutuzumab (VenO); we propose that venetoclax (Ven)-based therapy is generally preferable to BTKi with exception of TP53 aberrant disease. (5) BTKi-Ven versus VenO as preferred time-limited therapy; we discuss comparable efficacies and the concerns about simultaneous 1L exposure to both BTKi and Ven drug classes. (6) Utility of triplet therapy (BTKi-Ven-antiCD20 mAb) versus VenO; similar rates of complete response are observed yet with greater potential for adverse events. (7) Optimal therapy for TP53 aberrant CLL; while limited data are available, there are likely effective novel therapy combinations for TP53 aberrant disease including BTKi, BTKi-Ven ± antiCD20 mAb.

CONCLUSION

Frontline therapy for CLL should be selected based on efficacy considering the patient specific biologic profile of their disease and potential toxicities, considering patient comorbidities and preferences. With the present paradigm of sequencing effective agents, 1L combinations of novel therapies should be used with caution in view of potential adverse events and theoretical resistance mechanism concerns in the absence of compelling randomized data to support augmented efficacy.

The Evolution of Therapies Targeting Bruton Tyrosine Kinase for the Treatment of Chronic Lymphocytic Leukaemia: Future Perspectives

The development of inhibitors of Bruton tyrosine kinase (BTK) and B-cell lymphoma 2 (BCL2) has resulted in a paradigm shift in the treatment of chronic lymphocytic leukaemia (CLL) over the last decade. Observations regarding the importance of B-cell receptor signalling for the survival and proliferation of CLL cells led to the development of the first-in-class BTK inhibitor (BTKi), ibrutinib, for the treatment of CLL. Despite being better tolerated than chemoimmunotherapy, ibrutinib does have side effects, some of which are due to the off-target inhibition of kinases other than BTK. As a result, more specific inhibitors of BTK were developed, such as acalabrutinib and zanubrutinib, which have demonstrated equivalent/enhanced efficacy and improved tolerability in large randomized clinical trials. Despite the increased specificity for BTK, side effects and treatment resistance remain therapeutic challenges. As these drugs all bind covalently to BTK, an alternative approach was to develop noncovalent inhibitors of BTK, including pirtobrutinib and nemtabrutinib. The alternative mechanisms of BTK-binding of these agents has the potential to overcome resistance mutations, something that has been borne out in early clinical trial data. A further step in the clinical development of BTK inhibition has been the introduction of BTK degraders, which remove BTK by ubiquitination and proteasomal degradation, in marked contrast to BTK inhibition. This article will review the evolution of BTK inhibition for CLL and offer future perspectives on the sequencing of an increasing number of different agents, and how this may be impacted on by mutations in BTK itself and other kinases.

An update on the efficacy of Venetoclax for chronic lymphocytic leukemia

INTRODUCTION

The BCL2 inhibitor venetoclax has dramatically changed the treatment of chronic lymphocytic leukemia (CLL) and has introduced the concept of time-limited therapy with targeted agents.

AREAS COVERED

This review discusses the mechanism of action of venetoclax, adverse effects, and the clinical data with this agent as identified by a selective search of clinical trials in the PubMed database. Venetoclax is FDA-approved with anti-CD20 monoclonal antibodies; however, research is ongoing evaluating its efficacy when given in combination with other agents, such as the Bruton's Tyrosine Kinase (BTK) inhibitors.

EXPERT OPINION

Venetoclax-based therapy is an excellent treatment option for patients interested in time-limited therapy and can be offered in both the front-line and relapsed/refractory settings. Tumor lysis syndrome (TLS) risk evaluation, preventative measures, and strict monitoring should be conducted, while these patients ramp up to target dose. Venetoclax-based therapies produce deep and durable responses with patients often achieving undetectable measurable residual disease (uMRD). This has led to a discussion of MRD-driven, finite-duration treatment approaches, although longer term data is still needed. While many patients eventually lose uMRD status, re-treatment with venetoclax remains an area of interest with promising results. Mechanisms of resistance to venetoclax are being elucidated, and research is ongoing.

How We Manage Patients with Indolent B-Cell Malignancies on Bruton's Tyrosine Kinase Inhibitors: Practical Considerations for Nurses and Pharmacists

The most common forms of B-cell malignancy, non-Hodgkin lymphoma (NHL) and chronic lymphocytic leukemia (CLL), have seen a drastic shift in the treatment landscape over the last two decades with the introduction of targeted agents. Among them are Bruton's tyrosine kinase (BTK) inhibitors, which have demonstrated excellent efficacy in indolent B-cell NHLs and CLL. Although BTK inhibitors are generally thought to be more tolerable than chemoimmunotherapy, they are associated with a unique safety profile including varying rates of rash, diarrhea, musculoskeletal events, cardiovascular events, and bleeding. Ibrutinib was the first BTK inhibitor to gain a Health Canada indication, followed by second-generation BTK inhibitors acalabrutinib and zanubrutinib, which have better safety profiles compared to ibrutinib, likely due to their improved selectivity for BTK. As BTK inhibitors are oral agents given continuously until disease progression, long-term adverse event (AE) monitoring and management as well as polypharmacy considerations are important for maintaining patient quality of life. This paper intends to serve as a reference for Canadian nurses and pharmacists on dosing, co-administration, and AE management strategies when caring for patients with indolent B-cell NHL or CLL being treated with BTK inhibitors.

A History of Targeted Therapy Development and Progress in Novel-Novel Combinations for Chronic Lymphocytic Leukemia (CLL)

Over the last 10 years, the traditional treatment paradigms for CLL have been upended as the use of traditional chemoimmunotherapy regimens has declined in favor of novel targeted therapies. Targeted therapies have become the new standard of care in CLL given their superior progression-free survival (and overall survival, in some cases) when compared with chemoimmunotherapy, as well as their improved toxicity profiles. Targeted agents are FDA approved for the treatment of CLL including ibrutinib, acalabrutinib, zanubrutinib, and venetoclax. Importantly, as opposed to traditional chemotherapy regimens, the benefits of these targeted therapies appear to be consistent regardless of high-risk mutational status. In this review, we discuss the pivotal CLL studies of the last decade and the data supporting doublet and triplet novel-novel combinations. We explore the use of new surrogate end points for PFS/OS in targeted therapies such as undetectable minimal residual disease (uMRD) and their potential role in minimizing toxicity by permitting earlier treatment discontinuation. We also highlight areas that warrant further exploration and future studies that may help address some of these key questions.

Novel combination approaches with targeted agents in frontline chronic lymphocytic leukemia

Targeted therapies have revolutionized the frontline treatment landscape for patients with chronic lymphocytic leukemia (CLL) and have largely displaced a reliance on chemoimmunotherapy when treating this disease. Multiple randomized trials have documented the efficacy of oral therapy with the Bruton tyrosine kinase inhibitors ibrutinib and acalabrutinib (and zanubrutinib, pending a supplemental new drug application in CLL), as well as BCL2 inhibition using venetoclax. In this review, the authors highlight novel therapeutic strategies for using these agents in combination, either as doublet therapy or as triplet therapy, with anti-CD20 antibodies. First, the current treatment landscape is outlined, and the data are reviewed for continuous and time-limited therapeutic approaches, which constitute the current standard of care. Then, more recent reports are described from phase 2 and 3 studies exploring different combination strategies of Bruton tyrosine kinase and BCL2 inhibition for treatment-naive patients. In addition, relevant differences are emphasized between patient characteristics (e.g., patient fitness and the presence of high-risk disease features) and study methodology (e.g., dosing schedule, randomization, and assessment of measurable residual disease) across trials. Finally, the authors revisit the currently available data for these approaches in the context of ongoing studies and future planned trials, evaluating their potential impact on the frontline treatment landscape for CLL in the years to come.

Selecting initial therapy in CLL

Targeted therapy is a powerful treatment option in chronic lymphocytic leukemia (CLL) that has outperformed conventional chemoimmunotherapy in most clinical settings. Except for selected young, fit patients with a mutated immunoglobulin heavy chain variable region gene, most patients benefit from targeted therapy with either a continuous BTK inhibitor or 1-year fixed-duration venetoclax-obinutuzumab as first-line treatment of CLL. Treatment selection is driven by patient-, treatment-, and disease-related factors, encompassing patient preference, concomitant medications, comorbidities, safety profile of the regimen, and TP53 aberration. Clinical trials are actively investigating the simultaneous inhibition of Bruton's tyrosine kinase (BTK) and B-cell lymphoma 2 (BCL-2) proteins with or without a CD20 monoclonal antibody, which can achieve deep response in most patients (52%-89% undetectable minimal residual disease in bone marrow).

Real-World Persistence and Time to Next Treatment With Ibrutinib in Patients With Chronic Lymphocytic Leukemia/Small Lymphocytic Lymphoma Including Patients at High Risk for Atrial Fibrillation or Stroke

BACKGROUND

Atrial fibrillation (AF) is a recognized adverse consequence associated with all Bruton's tyrosine kinase inhibitors used to treat chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL); however, real-world time to discontinuation (TTD) and time to next treatment (TTNT) of CLL/SLL patients with a high baseline AF/stroke risk remain unknown.

MATERIALS AND METHODS

Patients with CLL/SLL from a nationwide electronic health record-derived database (February 12, 2013-January 31, 2021) initiating first-line (1L) or second or later-line (2L+) treatment with ibrutinib or other regimens on or after February 12, 2014 (index date) were analyzed. Kaplan-Meier survival analysis was used to assess TTD and TTNT among all patients, patients with high AF risk (CHARGE-AF risk score ≥10.0%), and patients at high risk of stroke (CHA₂DS₂-VASc risk score ≥3 [females] or ≥2 [males]).

RESULTS

In 1L/2L+, 2190/1851 patients received ibrutinib and 4388/4135, were treated with other regimens. Median TTD for ibrutinib was similar regardless of AF/stroke-related risk (1L: all patients, 15.7 months; high AF risk, 11.7 months; high stroke risk, 13.7 months; similar results in 2L+). Median TTNT was significantly longer for ibrutinib vs. other regimens (1L: not reached vs. 45.9 months; 2L+: not reached vs. 23.6 months; both P < .05), including among those with high AF/stroke risk. TTNT was similar between all patients and high-risk cohorts in 1L and 2L+ (all P > .05).

CONCLUSION

This study highlights that elevated baseline AF/stroke-related risk does not adversely impact TTD and TTNT outcomes associated with ibrutinib use. Additionally, TTNT was significantly longer for patients treated with ibrutinib vs. other regimens.