In the study, patients were randomized to venetoclax plus rituximab (VenR) or bendamustine plus rituximab (BR). Response was assessed clinically using complete blood count and physical examination at follow-up visits. PB MRD was analyzed centrally by allele-specific oligonucleotide polymerase chain reaction and/or flow cytometry at cycle 4, end of combination therapy, and every 3 months thereafter until 3 years, then every 6 months. Median follow-up was 36.0 months.
VenR patients achieved higher PB undetectable MRD (uMRD) rates (62%) compared with BR (13%) when combination therapy was completed. Likewise, observed uMRD rates were substantially different through month 24, when venetoclax single-agent treatment was scheduled to cease: 48% uMRD in VenR versus 2% in BR. Furthermore, consistently high uMRD rates were observed in all VenR subgroups, including patients with high-risk cytogenetics and molecular factors. Landmark analysis of PFS by MRD status in PB at the end of combination treatment response visit showed that MRD status was associated with longer PFS. At 2 years, 130 patients in the VenR arm completed treatment without disease progression. Of these patients, 83 (64%) were uMRD.
The data demonstrate the value of PB MRD as a predictive marker of clinical outcome for the chemotherapy-free regimen VenR, and confirm that the MRD rate is a meaningful end point for future research endeavors.
Kater AP, et al. ASH 2018. Abstract 695.