Continuous Clinical Remisssion with High MRD Negativity and High PB and BM MRD Concordance during Venetoclax Monotherapy in R/R CLL Patients

Introduction

Venetoclax, a novel BCL2 inhibitor, used either as monotherapy or in combinations, induces rapid disease control , with durable clinical remissions, especially in patients with deep responses. In the Venetoclax era, minimal residual disease(MRD) is a new endpoint in CLL studies. MRD negativity is associated with better clinical outcomes (Jain N, et al. ASH 2019, abstract 186, Tam CS, et al. ASH 2019, abstract 642).

Aim

We present our single-center MRD data from a cohort of patients with relapsed/refractory(RR) CLL, treated with venetoclax monotherapy.

Patients and Methods

We collected data from 24 R/R CLL patients who have been treated with venetoclax monotherapy until progression, in the context of VENICE-1 study (NCT02756611) in our department between 11/2016 and 1/2018. MRD was locally evaluated with 10-colour flow cytometry(FC) according to ERIC guidelines, with the cut off of <10^-4 (<0.01%) as negative, >10^-4-<10^-2 (>0.01%-<1%) as low-positive and >10^-2 (>1%) cut off as high-positive. Peripheral blood( PB) MRD was assessed every 3-6 months. At week48 (1 year), CT scans were performed for response assessment. Bone marrow (BM) biopsy and BM MRD at week48 were also performed in pts with CT confirmed CR.

Results

Between 11/2016 and 1/2018, 24 patients started treatment with venetoclax monotherapy. Our patients’ baseline characteristics are shown in table 1. Disease responses and patients’ treatment status as of end-July 2020 are shown in table 2. Progression free survival(PFS) and overall survival at 34 months is estimated 91.6% and 87.5% respectively. Four patients (16.7%) had to reduce their daily Venetoclax dose due to hematological toxicity: 2 to 300mg due to neutropenia and 2 to 200 and 100mg due to thrombocytopenia. MRD results at week 48 are shown in table 3. Sixteen patients have paired PB and BM MRD results (15 at week 48 and 1 at week 24) with 87.5% concordance (14 patients). In seven MRD negative patients MRD conversion (2 consecutive samples) was observed, after a median time of 16 m(6-28): six patients to low-positive and one to high-positive. The high-positive MRD-converted patient presented clinical relapse at the 2^nd high-MRD positive sample, according to iwCLL criteria. One of 6 low-positive MRD-converted patients, became MRD negative again at a later time-point.

Conclusion

Our single-center data from 24 CLL patients enrolled in the Venice-1 study reveal high concordance of PB and BM MRD at week48. Higher PB MRD negativity rate at week 48 is observed (79.2%) in comparison to Venice trial (Kater A, et al. EHA 2020, S156) due to differences in MRD methodology/number of evaluable patients. Our FC MRD data show that MRD conversion from negative to low-positive may be observed during continuous Venetoclax treatment, without clinical disease progression. This observation, along with high PFS at 34 months (91.5%) confirms the importance of continuing Venetoclax therapy in RR CLL patients when given as monotherapy.