ISHL12 Abstract 59

Circulating tumor DNA in classical Hodgkin lymphoma patients treated with pembrolizumab and chemotherapy: dynamic response assessment and correlation with baseline total metabolic tumor volume

Introduction: We have previously presented early results of untreated CHL patients treated with concurrent pembrolizumab + AVD (Lynch et al. ASH 2021) which had increased rates of false positive PET/CT results leading to additional scans and/or biopsies. Circulating tumor DNA (ctDNA) may represent a more sensitive and specific method of response assessment. Herein we report updated clinical results with correlation of dynamic ctDNA monitoring as well as data on total metabolic tumor volume (TMTV).

Methods: This was a single arm pilot study combining pembrolizumab with AVD in untreated CHL of any stage. Plasma 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 CAPP-Seq and PhasED-Seq (Kurtz et al. Nat Biotech 2021). Baseline, post cycle 2, and end of treatment PET/CT were analyzed for TMTV using a threshold based semiautomated technique that included any tumor with standardized uptake value (SUV) above the liver background SUVmax using MIM Encore (version 7.1.3 Cleveland, OH).

Results: Among the 30 patients enrolled, 29 are evaluable for response and/or exploratory analysis. With median follow-up of 21 months, 2-year PFS and OS were 97% and 100%, respectively. While 5 patients had residual FDG uptake at EOT, only 1 (20%) has developed recurrent lymphoma. ctDNA data was available for 18 patients. Pretreatment ctDNA levels were significantly correlated with TMTV (RS=0.68, p=0.003). 17/18 patients had detectable ctDNA at baseline and were therefore evaluable for MRD assessment. Among 8 PET2+ patients, only 1 patient had detectable ctDNA, and ctDNA became undetectable by the end of treatment. Importantly, of these 8 patients, none have relapsed. Only 1/9 (11%) patients who were PET2- had detectable ctDNA after 2 cycles, and the cancer ultimately recurred. At EOT for those who received > 2 cycles, 2/14 had detectable ctDNA (one CHL relapse, one with secondary DLBCL 11 months later). ctDNA analyses for the remaining patients are in process and will be presented at the meeting.

Conclusion: Concurrent pembrolizumab + AVD represents highly effective frontline therapy for CHL, but results in spurious PET findings in a significant proportion of patients despite most patients having undetectable ctDNA and no relapse. ctDNA may represent a more sensitive and specific response assessment tool to be studied in larger datasets.