Circulating Tumor DNA Dynamics as Early Outcome Predictors for Lisocabtagene Maraleucel as Second-Line Therapy for Large B-Cell Lymphoma from the Phase 3 TRANSFORM Study

Background: While the prognostic value of MRD using ultrasensitive circulating tumor DNA (ctDNA) assays after first-line immunochemotherapy for DLBCL has been shown (Roschewski M, et al. Blood 2022;140[suppl 1]:785), its relevance to outcomes after second-line (2L) treatment with CD19-directed CAR T cell therapy remains unclear. The phase 3 TRANSFORM study (NCT03575351) showed statistically significant and clinically meaningful improvements in event-free survival (EFS), CR rate, and PFS for lisocabtagene maraleucel (liso-cel) compared with standard of care (SOC) for patients (pts) with primary refractory or early relapsed large B-cell lymphoma (LBCL) eligible for autologous HSCT (Kamdar M, et al. Lancet 2022; Abramson JS, et al. Blood 2023). Here, we report longitudinally measured ctDNA levels from TRANSFORM as a prospective measure of disease burden and describe the predictive value of ctDNA after 2L liso-cel therapy for LBCL.

Methods: From the original randomized population (n = 184), 551 plasma samples from 160 pts (liso-cel, n = 79; SOC, n = 81) were used for ctDNA assessment in a blinded manner by Phased Variant (PV) Enrichment and Detection Sequencing (PhasED-Seq) at Foresight Diagnostics. Tumor-derived PVs were identified directly from baseline plasma samples taken at screening without use of tumor tissue; matched DNA from peripheral blood mononuclear cells was used to censor germline variants and clonal hematopoiesis. PVs were used to longitudinally assess ctDNA on the day of liso-cel infusion; at Day 15; and Months 1, 2, 3, and 12 after infusion. For the SOC arm, only pretreatment samples were evaluated. ctDNA levels were compared with baseline characteristics, responses by Lugano 2014 criteria, and EFS. Pts/samples were reported as having detectable MRD when ctDNA levels exceeded a detection threshold (≈1:10⁶ cell-free DNA molecules) corresponding to 98% specificity.

Results: PVs were identified from 136 of 160 pts (85%) with evaluable pretreatment samples from the liso-cel and SOC treatment arms. The remaining samples had lower disease burden (sum of product of diameters [SPD]; 13%) or failed quality check (2%). Pretreatment ctDNA levels varied widely (median [IQR]: 136 [35‒696] haploid genome equivalents/mL) and were correlated with disease indices portraying higher-risk disease, including stage (P = 0.02), age-adjusted International Prognostic Index (P < 0.0001), disease burden (SPD; P < 0.0001), and LDH (P < 0.0001).

Serial ctDNA levels were evaluated after liso-cel infusion in 63 pts. Achieving undetectable ctDNA was associated with achieving CR and longer EFS at all time points after liso-cel infusion. ctDNA levels decreased rapidly in pts who achieved CR at Month 3, with 50% (17/34) having undetectable ctDNA by Day 15 after liso-cel infusion. Conversely, 89% of pts (16/18) with PD at Month 3 still had detectable ctDNA at Day 15 with lower levels of ctDNA clearance. These results highlight significant enrichment of undetectable ctDNA observed as early as Day 15 after infusion between pts with Month 3 CR versus PD (P = 0.006). ctDNA clearance in pts who achieved CR at Month 3 continued to deepen further over time, with undetectable ctDNA rates of 63%, 74%, and 86% at 1, 3, and 12 months after liso-cel infusion, respectively. Furthermore, most pts in CR by PET/CT had undetectable ctDNA at paired time points (71%), confirming that pts achieving CR also achieved durable molecular remission. In the cases with discordant CR and ctDNA results, detection of residual ctDNA was significantly prognostic for shorter EFS at all respective response assessments (fraction of CR cases with residual ctDNA at 1 month and Log-rank test P value for EFS: 47% [15/32], P = 0.011; 3 months: 26% [9/34], P = 0.025; 12 months: 13% [4/31], P = 0.003).

Conclusions: Achieving undetectable ctDNA in the first 3 months and as early as 15 days after liso-cel infusion was significantly associated with durable clinical benefit. Conversely, detectable ctDNA captured relapse risk unmeasured by imaging. These results demonstrate the potential clinical value of ctDNA monitoring as a biomarker for disease surveillance and as an early predictor of clinical benefit of liso-cel treatment for LBCL, which could guide and accelerate future clinical trials.