Phase II Study of Venetoclax in Combination with Obinutuzumab and Bendamustine in Patients with High Tumor Burden Follicular Lymphoma As Front Line Therapy (PrECOG 0403)

Background:

Chemoimmunotherapy is considered standard initial therapy for follicular lymphoma (FL) with high tumor burden (HTB). Obinutuzumab and Bendamustine (OB) with maintenance Obinutuzumab (mO) is considered a standard therapy for the frontline treatment of HTB FL (GALLIUM, Marcus et al, NEJM 2017). Venetoclax (VEN), an oral BCL2 inhibitor, is an attractive target in FL given the high BCL2 expression; though single agent activity has been disappointing (Davids et al. JCO 2017). BCL2 inhibition is thought to be synergistic with chemotherapy. Thus, the PrE0403 study evaluated the OB-VEN combination in frontline HTB FL. Here we present end of induction (EOI) outcomes.

Methods:

The primary objective of this Phase II study was to estimate the complete remission (CR) rate at EOI. Potential participants must have had a histologically confirmed diagnosis of FL grade 1, 2, or 3a with HTB defined by GELF or high risk defined by FLIPI-1 criteria. They must have had adequate performance status and organ function. Notably, creatinine clearance must have been ≥50 mL/min. Participants must have not had prior treatment for FL.

Eligible participants were treated with Bendamustine IV 90 mg/m2 Day (D) 1 & 2, Obinutuzumab IV 100 mg D1, 900 mg D2, 1000 mg D8 and D15 of Cycle (C) 1 then D1 of each cycle, and VEN 800 mg orally daily D1-10 every 28 days for 6 total cycles. Due to a high rate of laboratory tumor lysis syndrome (TLS) during C1 in the first 21 patients, VEN was removed from C1 and given in C2-6 only. Participants with a CR at EOI were treated with mO IV 1000 mg D1 every 8 weeks for 2 years. Those with a partial response (PR) or stable disease (SD) were treated with mO as well as VEN 800 mg orally daily for 2 years. Pneumocystis jiroveci Pneumonia (PJP) and antiviral prophylaxis was required as was G-CSF support.

Response was assessed via Lugano Criteria at EOI including PET/CT and bone marrow assessment. Adverse Events (AEs) were evaluated using CTCAE v5.0. To be considered promising, OB-VEN should improve the null hypothesis CR rate of 50% (OB) to 65%. With an 85% power and a one sided 15% type I error, 56 participants would be needed with an estimated 51 eligible.

Support for the study was from Genentech, Member of the Roche Group.

Results

A total of 56 participants were enrolled and treated between 12/2017 and 11/2020; baseline characteristics are listed in Table 1. TLS was closely monitored in C1 and 8/21 participants developed TLS when VEN was administered in C1; 0/35 when it was not. However, monitoring for TLS in C1 became less stringent when VEN was not administered. Treatment related Grade ≥3 toxicities occurred in 47/56 participants (83.9%) with serious adverse events in 31 of 56 (55.5%). Atypical infections were seen; there was one treatment related death on study due to cytomegalovirus (CMV) encephalitis as well as PJP pneumonia which occurred after induction C6. Enrollment was temporarily suspended and CMV monitoring was implemented with no further occurrences. Another participant receiving mO later developed BK virus nephropathy following mO C6 and now requires ongoing hemodialysis. Another was diagnosed with Respiratory Syncytial Virus pneumonia 30 days after C6 and later PJP pneumonia after C2 of mO. Common (incidence >10%) AEs during induction are listed in Table 2. 45 of 56 (80.4%) participants were able to receive all 6 cycles of OB-VEN.

CR was seen in 41 of 56 participants (73.2%, 2 sided 95% Confidence Interval (CI) 59.7-84.2%) at the EOI. 30 participants (53.5%) went onto maintenance. With a median follow up of 20.9 months, estimated 2 year Overall Survival (OS) and Progression-Free Survival (PFS) (90% CI) is 94.4% (82.4-98.3%) and 85.8% (68.8-93.9%) respectively.

Conclusions

This Phase II study of OB-VEN in untreated HTB FL showed high CR rate and met its primary endpoint with early signs of prolonged PFS. Laboratory TLS was identified but it was unclear if attributed solely to VEN, as baseline laboratory TLS rate for OB is unknown. The rate of Grade ≥3 AE of 83.9% (compared to 69% for OB in GALLIUM, Hiddeman JCO 2018) and the observation of opportunistic infections including CMV encephalitis, PJP pneumonia and BK nephropathy, suggests the combination is highly immunosuppressive. Therefore, while the study met its primary outcome, the combination of OB-VEN at 800 mg for 10 days, plus mO, does not have an acceptable risk/benefit profile. Participants will continue to be followed for efficacy and safety during the maintenance phase.

Figure 1

View largeDownload slide

Figure 1

View largeDownload slide

Close modal