Abstract 5071: Minimal residual disease (MRD) status by peripheral blood mononuclear cells (PBMCs) and circulating tumor DNA (ctDNA) demonstrates rapid, deep, and sustained response in patients (Pts) with relapsed/refractory follicular lymphoma (R/R FL) treated with subcutaneous (SC) epcoritamab monotherapy in the pivotal phase 1/2 EPCORE™ NHL-1 trial

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Abstract Introduction: Outcomes in high-risk R/R FL are poor. Epcoritamab SC, a CD3xCD20 bispecific antibody, demonstrated promising efficacy with a manageable safety profile in pts with R/R FL after ≥2 prior lines of therapy (phase 1/2 EPCORE NHL-1; NCT03625037). Here we evaluated MRD with PBMCs and ctDNA in pts with R/R FL and correlated the results with clinical findings. Methods: Adults with R/R FL 1-3A enrolled in EPCORE NHL-1 received epcoritamab SC in 28-day cycles. MRD analysis was performed on longitudinal plasma and PBMC samples collected at prespecified timepoints (clonoSEQ assay, Adaptive Biotechnologies). Screening tumor biopsies were used to identify trackable tumor clones; samples were quantified as tumor clones detected per mL plasma for ctDNA and per one million nucleated cells for PBMC. Overall response and progression-free survival (PFS) were assessed using Lugano criteria by independent review committee. Results: Of 128 pts in the R/R FL 1-3A cohort, 91 with PBMC data and 100 with ctDNA data were MRD evaluable. Overall MRD negativity was achieved in 67.0% [95% CI: 56.4-76.5] of pts per PBMC and 68.0% [95% CI: 57.9-77.0] of pts per ctDNA. Concordance of subject-level MRD status was high (79 of 89 with PBMC and ctDNA data; 88.8%). In most pts, MRD negativity was reached prior to radiographic complete response (PBMC, 76.4%; ctDNA 58.5%). MRD negativity by PBMC preceded ctDNA (median days to MRD negativity, 28 [PBMC] vs 57 [ctDNA]), suggesting a difference in methodology in detecting tumor DNA. Pts who became MRD negative had prolonged PFS (median not reached). Baseline MRD levels were not associated with clinical outcomes (PBMC; Wilcoxon P=0.59, ctDNA P=0.39). PFS was similar in pts achieving MRD negative status (median not reached, PBMC and ctDNA), independent of high-risk/difficult-to-treat disease (≥4 prior lines, Ann Arbor stage III-IV, bulky disease, double refractory, FLIPI 3-5, and POD24). The overall MRD negativity rate was also similar in high-risk pts, except those with ≥4 prior lines of therapy. Conclusions: Based on the EPCORE-NHL-1 study, one of the first pivotal studies to report MRD in pts with R/R FL, epcoritamab drives rapid, deep, and sustained responses as supported by MRD assessment by both PBMC and ctDNA. MRD results correlate with clinical outcome, and achieving MRD negativity is associated with longer PFS. PFS was similar among all pts who achieved MRD negativity, including those with high-risk disease. Citation Format: David Soong, Işıl Altıntaş, John Karavitis, Kim M. Linton, Wojciech Jurczak, Catherine Thieblemont, Kevin Zhao, Edith Szafer-Glusman, Daniela Hoehn, Elena Favaro, Mariana Sacchi, Maria Jure-Kunkel. Minimal residual disease (MRD) status by peripheral blood mononuclear cells (PBMCs) and circulating tumor DNA (ctDNA) demonstrates rapid, deep, and sustained response in patients (Pts) with relapsed/refractory follicular lymphoma (R/R FL) treated with subcutaneous (SC) epcoritamab monotherapy in the pivotal phase 1/2 EPCORE™ NHL-1 trial [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5071.