High Rates of Undetectable MRD By Phased-Seq on Interim and End of Treatment Timepoints in Untreated Advanced Stage Chl Treated with Pembrolizumab + AVD

Introduction We previously reported initial (n=30) efficacy results of a frontline study of pembrolizumab + AVD (Lynch et al Blood 2023, ASH 2023) in classic Hodgkin lymphoma (CHL). Despite finding surprisingly high rates of positive interim and EOT PET/CT compared to historical data, observed outcomes were excellent. Herein we present updated clinical data for our full 50-patient study including interim and end of treatment (EOT) MRD testing by PhasED-Seq Methods We examined additional long-term follow up of patients with pembrolizumab combined with concurrent AVD in previously untreated CHL as previously described (NCT03331341). Samples were analyzed for ctDNA at baseline, post cycle 1 (if available), post cycle 2, and end of treatment. ctDNA levels were quantified as haploid genome equivalents/mL plasma using PhasED-Seq (Kurtz et al. Nat Biotech 2021). Results 50 patients were enrolled between Feb 1, 2019, and Apr 13, 2023, with a median follow up of 3.1 years; 3-year PFS and OS were 98% and 100%, respectively. Among advanced stage patients (n=38), 3-year PFS and OS were 97% and 100%, respectively. In patients where samples were available for analysis, baseline ctDNA was detectable in 11/12 (92%) of early-stage patients, and 36/37 (97%) of advanced stage patients. 7/8 (88%) early-stage patients had undetectable MRD (uMRD) at C3D1, and all cleared ctDNA by EOT and none have relapsed to date. Among advanced stage patients, 22/29 (76%) of samples at C2D1 and 29/35 (83%) samples at C3D1 had uMRD. In contrast, the PET CR rate at C3D1 in advanced stage patients was only 58%. At EOT, 31/34 (91%) advanced stage samples had uMRD compared to a PET CR rate of 73%. The only patient in the study to relapse had a negative interim PET but did not clear ctDNA at any timepoint. Two additional patients had minute amounts of ctDNA detectable at the end of treatment after levels dropped >20,000 fold when compared to baseline. Both patients have not relapsed 3 years and 14 months after completion of treatment, respectively. Some timepoints did not have plasma samples available, and no samples were drawn for sequencing during follow-up, Conclusion Pembrolizumab + AVD continues to demonstrate durable efficacy in previously untreated CHL. No patient who has cleared ctDNA as measured by PhasED-Seq has relapsed to date despite high rates of interim-PET and EOT PET positivity. The role of PhasED-Seq will be further examined in the upcoming Phase 2 MRD-adapted PRECISE-HL study in untreated advanced stage CHL.