Changes In Circulating Tumor Dna Levels Are Associated With Treatment Response And Progression-Free Survival In Relapse/Refractory Dlbcl Subjects.

7546 Background: Detection of an initial molecular response to therapy in DLBCL could help differentiate patients who will relapse (30-40% of frontline subjects) from those who will not. Recent studies in DLBCL showed ability to detect residual disease and molecular response to therapy from analysis of circulating tumor DNA (ctDNA). Here we performed targeted next generation sequencing (NGS) of baseline ctDNA vs. tumor tissue, and on-treatment ctDNA samples in 32 relapse/refractory DLBCL subjects from the ROMULUS study to assess correlation of outcome with molecular response. Methods: We sequenced plasma, plasma depleted whole blood (PDWB), and tumor DNA from 32 subjects (range 2-6 samples / subject). Library preparation and NGS were performed using hybrid capture-based workflows, with a panel of ~300 kb targeting regions relevant for disease detection in DLBCL. Variants were called from tissue and plasma data, and PDWB data were used to filter out non-tumor specific variants. Results: 83% of variants detected in tissue (1441/1745) were found in the corresponding plasma samples, and 78% of variants detected in plasma (1441/1846) were found in corresponding tissue samples, in line with previous reports. To follow ctDNA changes with treatment, tumor-specific variants were determined from tissue or cycle 1 day 1 (C1D1) plasma samples. These variants were then monitored in C1D1 and later timepoints, with similar ctDNA levels based on variants determined from C1D1 plasma or tissue (R2=0.99). Change in ctDNA levels from C1D1 to C2D1 separated subjects that responded from subjects that progressed (Wilcoxon p-value: 9.39×10-4). Subjects that showed a 10-fold or higher drop in ctDNA levels between C1D1 and C2D1 had significantly longer PFS than those with a smaller ctDNA fold change (HR: 8.06; p=0.0008). Conclusions: This study showed that tumor-specific variants can be identified in baseline plasma with similar performance as from tumor tissue, and that monitoring molecular response as an early change in ctDNA levels after one cycle of treatment correlated with outcomes in this DLBCL study. Clinical trial information: NCT01691898.