Detection of molecular residual disease (MRD) for cancer management: Lessons from longitudinal profiling of NSCLC patients undergoing chemotherapy or targeted therapy.

e15020 Background: Identification of cancer patients who are at ongoing risk of relapse remains of high priority to direct effective adjuvant therapy. Plasma circulating cell-free DNA (cfDNA) analyses offer an unprecedented approach to identify patients with molecular residual disease (MRD) earlier than clinical or radiological evidence, detecting drug resistance, progression and relapse with relatively high sensitivity and specificity. Here we used longitudinal surveillance to profile cfDNA mutational landscape undergoing chemotherapy or EGFR-TKI. We demonstrated how cutting-edge NGS and digital qPCR technologies are defining new subgroups of patients with MRD for individually tailored treatment strategy. Methods: Plasma samples were collected from 8 subjects with lung adenocarcinoma, 5 patients were treated with EGFR-TKI and 3 cases by chemotherapy. Overall, 92 longitudinally collected specimens (duration of 31-143 weeks) were analyzed with a 520-gene ultra-deep NGS platform as well as a digital qPCR assay. Standard-of-care tests of CEA, CA19-9 biomarkers and CT radiography were also performed in parallel. Results: The number of somatic mutations detected ranging from 0 to 52 in a sample and correlated strongly with TMB (tumor mutational burden). The concordance of actionable EGFR mutations (L858R, T790M, Ex19Del) detected by NGS and digital qPCR assays was 100% (n = 49/49). NGS assay detected additional driver mutations in ∼20 non-EGFR genes. Majority of EGFR mutations showed directional decline in allelic fraction (AF) after treatment with EGFR-TKI. Patient progressed following EGFR-TKI were registered to undergo chemotherapy based on real-time mutational profiles and did show good responses and PFS. Longitudinal ultra-deep NGS analyses can help detect and stratify MRD, including non-druggable genetic information that could guide best clinical decision-making. Conclusions: Longitudinal ctDNA surveillance of patients treated with EGFR-TKI by a highly sensitive multi-gene NGS panel enables MRD monitoring and can potentially guide a selection of optimal adjuvant therapies earlier, and provide new surrogate endpoints for early registration of these therapies.