Phased Variant–Supported Circulating Tumor DNA as a Prognostic Biomarker After First-Line Treatment in Large B-Cell Lymphoma: Findings From the DIRECT Study

PURPOSE Circulating tumor DNA (ctDNA) is emerging as a promising tool to monitor treatment response in large B-cell lymphoma (LBCL). Tracking tumor-specific phased variants (PVs) allows ultrasensitive detection of minimal residual disease (MRD) that may enhance the accuracy of response assessment. Previous studies have been constrained by small cohort size, retrospective design, or assays limited to a single commercial provider. PATIENTS AND METHODS DIRECT was a prospective, multisite study evaluating the utility of ctDNA in patients with LBCL. We developed a lymphoma-customized, open-source, ctDNA assay and pipeline that captured hundreds of PVs per patient. Using landmark analysis, we evaluated the prognostic impact of PV-supported MRD at the end of first-line therapy (EoT). RESULTS EoT PV-MRD status was available for 155 patients. After a median of 24.5 months, 2-year time to tumor progression (TTP) for patients with detectable versus undetectable PV-MRD was 42% versus 95%, respectively ( P < .001; hazard ratio [HR], 13.7). When restricted to patients receiving full-dose anthracycline-based immunochemotherapy, 2-year TTP was 45% versus 96%, respectively ( P < .001; HR, 15.4), outperforming conventional radiological response assessment (HRs, 6.9 for positron emission tomography v 16.9 for PV-MRD). The limit of detection with 95% confidence (LoD95) varied by more than two orders of magnitude across patients, underscoring the need to report patient-specific LoD95. Persistent PV-MRD in the absence of relapse was noted, including three of four patients with transformed follicular lymphoma, highlighting a potential caveat when interpreting positive PV-MRD . CONCLUSION EoT PV-MRD enables sensitive and clinically meaningful response assessment in LBCL. It provides independent prognostic information, enhancing EoT response assessment beyond conventional radiologic assessment. Our findings support the incorporation of PV-MRD into clinical trials and routine management of diffuse LBCL.