Phase II study of venetoclax added to bendamustine and obinutuzumab in patients with high-risk follicular lymphoma as front-line therapy: PrE0403.

Over-expression of BCL-2 defines follicular lymphoma (FL). Venetoclax (VEN), a selective BCL-2 inhibitor, has previously been evaluated with bendamustine-based chemoimmunotherapy. VEN was given continuously, resulting in promising efficacy but unacceptable toxicity. The Phase II PrE0403 study was designed to evaluate intermittent dosing of VEN (10 days per cycle) combined with obinutuzumab and bendamustine (VEN-OB) in untreated FL subjects with high-risk features defined as a FLIPI-1 score of ≥3 and/or high tumor burden by GELF criteria. A total of 56 subjects were planned to be accrued with a goal of having 51 subjects eligible to improve the historical 50% CR rate to 65% with an 85% power and 15% type I error rate. Immunohistochemistry (IHC) expression of 3 antiapoptotic proteins (BCL-xL, MCL-1, and BCL-2) was performed and correlated with clinical outcomes. All 56 subjects were eligible and treated. CR rate was 41/56 (73.2%) and ORR was 52/56 (92.5%) meeting the primary endpoint. 2-year estimated PFS was 87.5% (90% CI: 75.3,93.9%) and 2-year estimated OS was 94.6% (90% CI: 86.7, 97.9%). However, the incidence of treatment-related adverse events ≥ grade 3 was 83.9% and serious adverse events were seen in 57.1%. After induction, atypical infections, including Grade 5 events, occurred. Anti-apoptotic protein expression by IHC was not correlated with clinical outcomes. Thus, while meeting the primary efficacy end point, VEN-OB is considered overly toxic in high-risk FL.