Evaluation and associated risk factors for neutropenia with venetoclax and obinutuzumab in the treatment of chronic lymphocytic leukemia

Abstract Background The time‐limited combination of venetoclax and obinutuzumab (VenG) was established by the German CLL Study Group in the CLL14 trial for the upfront management of newly diagnosed chronic lymphocytic leukemia (CLL), showing a superior progression free survival benefit. The incidence of grade 3–4 neutropenia was reported in the range of 52.8%–57.7%. However, patients who develop neutropenia with this combination have yet to be formally characterized in the literature as it has impact on the clinical practice setting. Aim To determine the incidence of grade 3 and 4 neutropenia and identify risk factors for neutropenia among CLL patients treated with the VenG regimen. Methods We conducted a retrospective, single‐center study of all adult patients with a diagnosis of CLL treated with VenG at the University of Colorado Hospital. Demographic information, laboratory data, clinical data, and medication prescriptions were collected from the patients' electronic medical record. Results A total of 14 patients (73%) developed neutropenia during the course of therapy. The mean time to neutropenia from the start of treatment was 42 days (range 1–131). Our cohort harbored more high risk disease features and more comorbidities (CIRS score of 12). Four patients (28.6%) in the neutropenic group developed infectious complications during therapy and 6 (31%) patients were unable to be dose escalated to the final FDA approved dose of 400 mg. Conclusion Our study cohort had higher incidence of grade 3 and 4 neutropenia occurring in 73% of patients. This could be attributed to a higher rate of comorbidities, high risk features, concomitant interacting medications, and prior chemotherapy. Further studies are warranted to determine if growth factor support is efficacious to achieve dose escalation with this therapy.


| INTRODUCTION
Treatment of Chronic Lymphocytic Leukemia (CLL) has radically transformed over the past decade with the advent of targeted therapies.
The addition of these molecularly targeted therapeutics, as compared to chemotherapy agents, have improved survival and tolerability. [1][2][3][4] Venetoclax is an oral selective B-cell lymphoma 2 (BCL2) inhibitor, an important antiapoptotic protein expressed on B-cells. Venetoclax promotes cell death by disrupting antiapoptotic cell signaling. 5,6 Obinutuzumab, an anti-CD20 antibody, in combination with venetoclax (VenG) was established by the German CLL Study Group in the CLL14 trial, showing a superior progression free survival benefit. 1 This combination has been an attractive option for patients as it allows for a fixed duration of treatment when compared to the continuous administration necessary for other targeted oral agents, including the Bruton's tyrosine kinase inhibitors and the phosphatidylinositol-3 kinase inhibitors. 1,4 While venetoclax is a more selective BCL2 inhibitor, lacking the dose limiting thrombocytopenia of its predecessor navitoclax, neutropenia remains a concern. 6-8 Neutropenia has been reported in the phase 3 studies. The incidence of grade 3-4 neutropenia reported in CLL-14 was reported to be 52.8%, and 58% at long term follow up. 1,9,10 By contrast, the MURANO trial examined the use of an anti-CD20 agent with venetoclax in the relapsed refractory setting and found the incidence of grade 3-4 neutropenia to be 57.7%. 4 Data with respect to real world incidence of neutropenia is sparse. Davids et al report their experience with venetoclax monotherapy in the relapsed/refractory setting and characterize additional risk factors in this population. This analysis found patients, classified as high risk (Binet stage C and a neutrophil count <5.64 Â 10 9 /L or Binet stage A/B and neutrophil count <2.46 Â 10 9 /L), to have a reported rate of grade 3 and 4 neutropenia of 83%. 11

| Patients
Patients were included if they had a diagnosis of CLL and were treated with the regimen of VenG. Patients could have received treatment in the frontline or relapsed/refractory setting but must have received venetoclax in combination with obinutuzumab. Patients with incomplete medical records were excluded.

| Data collection
Demographic and clinical data were collected from the patients' electronic medical record including age, gender, race, prior radiation history, and number of prior therapies. Prognostic factors collected included Rai stage, immunoglobulin heavy chain rearrangement status, lymph node size, next generation sequencing, and fluorescence in situ hybridization testing. Pertinent labs were recorded immediately prior to VenG initiation (Table 1) and followed until end of therapy. Neutropenia in this study was defined as an absolute neutrophil count less than 1000/mm 3 as defined by the Common Terminology Criteria for Adverse Events. 9 Prior medication data including concomitant cytochrome P450 (CYP) 3A4 inhibitors and inducers, p-glycoprotein (P-gP) inhibitors, as well as granulocyte colony stimulating factors were captured. Descriptive statistics were used for all outcomes.

| Patient characteristics
We identified 19 patients eligible for review who were predominantly Caucasian (94.7%) and male (57.9%). The patient demographics at initiation of VenG can be found in

| Neutropenia
A total of 14 patients (73%) developed neutropenia during the course of therapy. The median time to neutropenia from the start of treatment was 42 days (range 1-131). Seven patients received prior therapy and six of those patients (86%) developed neutropenia. This is in contrast to those who received VenG as upfront therapy in which eight patients (66%) experienced neutropenia. A summary of these outcomes are listed in Table 3.
Four patients (28.6%) in the neutropenic group developed infectious complications during therapy, as compared to one patient in the non-neutropenic group. This included two (10%) bacterial pneumonias, one (5%) septic arthritis, one (5%) fungal infec-

| DISCUSSION
The prior published studies describing phase 3 data utilizing an anti- The addition of monoclonal antibodies, such as anti-CD20 agents, have been known to be an independent factor for neutropenia both with and without chemotherapy. 14,15 This should be considered as a compounding factor for higher rates of neutropenia in this setting.
Obinutuzumab also appears to be associated with higher rates of neutropenia as compared to its counterpart, rituximab. 15 This was reflected in our cohort with a median onset to neutropenia of 42 days and at a median venetoclax dose of 20 mg. Additionally, consideration should be taken when using these antibodies in the relapsed/refractory setting as studies have shown a higher incidence of neutropenia when compared to patients in the frontline setting. 16,17 Prescribing information for venetoclax have specified dose modifications for hematologic toxicities, however the recommendations provided for Obinutuzumab are less distinct. 5,18,19 Management of neutropenia in this setting can involve dose interruption, reduction and/or growth factor support. 20 A post hoc analysis of the MURANO study found that venetoclax treatment dose reduction or interruption for adverse effects had no effect on progression free survival outcomes. 20 In contrast, treatment discontinuation was associated with inferior PFS outcomes. This highlights the importance of prompt management of adverse effects, including neutropenia, to maximize treatment duration and avoid therapy discontinuation. 20 Furthermore, currently no guideline exists for initiation of growth factor in this particular population but is left to the discretion of the provider. 14 31.6% of our cohort received growth factor support, and of those receiving growth factor (n = 6), all but one patient was able to complete the venetoclax dose escalation to the final 400 mg dose. The small sample size and retrospective nature of our study makes it difficult to extrapolate the benefit of this approach to a wider population, but does warrant further study.
Finally, additional consideration should be made regarding the effect of concomitant medications, particularly agents affecting CYP3A4 or P-gP. Azole antifungals are used for prevention of fungal infections in at risk patients, but are also known inhibitors of CYP3A4.
Moderate inhibitors, such as fluconazole, would require a 50% dose reduction in venetoclax per the prescribing information. 5 Our retrospective chart review had a low-rate azole prophylaxis (n = 4), and

ACKNOWLEDGMENTS
All authors have read and approved the final version of this manuscript.

CONFLICT OF INTEREST
Manali Kamdar reports research funding from TG Therapeutics, Genetech and personal fees from AbbVie, KaryoPharm, Kite, AstraZeneca, Celgene/Bristol-Myers Squibb, Adaptive Biotechnologies, and ADC therapeutics. The authors report no other conflicts of interest.

AUTHORS' CONTRIBUTIONS
All authors had full access to the data in the study and take responsibility for the integrity of the data and the accuracy of the data analy-

ETHICAL STATEMENTS
University of Colorado Institutional Review Board (IRB#20-2774) waived the need for ethics approval and the need to obtain consent for the collection, analysis and publication of the retrospectively obtained and anonymized data for this non-interventional study.

DATA AVAILABILITY STATEMENT
The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.