Abstract 736: ctDNA detection in early stage non-small cell lung cancer

Introduction Overall survival of non-small-cell lung cancer (NSCLC) patients remains poor as patients are frequently diagnosed at late stage. The evaluation of circulating tumor DNA (ctDNA) has been shown to offer a non-invasive method for cancer detection. However, detection rates of ctDNA in patients with early stage cancers have been low. The distribution of ctDNA levels in this population is unknown, and the analytical requirements for a test to detect the majority of cancers cannot be defined. Methods The LUCID study (LUng cancer - CIrculating tumour DNA study) recruited 100 patients with stage I-IIIB NSCLC according to the TNM 7th edition and collected plasma samples before and after radical treatment by surgery or radiotherapy +/- chemotherapy with curative intent. To measure levels of ctDNA in patients with early stage disease and very low tumor burden we developed a method for INtegration of VAriant Reads (INVAR), which uses sequencing data across hundreds to thousands of tumor-mutated loci to detect ctDNA in plasma samples at high sensitivity. We applied INVAR to 90 of the patients from the LUCID study, where tumor sequencing data was available. To measure ctDNA in the remaining LUCID patients, we applied the InVision® amplicon-based plasma sequencing assay. Results Across the 100 patients, ctDNA signals were observed in 67% of samples obtained prior to treatment. ctDNA was detected in 66% of cases, with ctDNA levels as low as 9.1x10-6 (9 parts per million), at a detection threshold with 95% specificity. ctDNA was detected in 52% of 60 patients with stage I NSCLC and in 88% of 40 patients with stage II/III disease. Analyzing different histological subtypes, ctDNA was detected in 79% of squamous cell carcinomas and 60% of adenocarcinomas. We found a good agreement when comparing the ctDNA results obtained from INVAR and the InVision® assay. Conclusions Our findings suggest that an assay with sensitivity to below 10 parts per million may be able to detect ctDNA in as many as 2/3 of patients with early stage NSCLC prior to treatment, including the majority of adenocarcinoma cases. Additionally, patient-specific analysis of ctDNA has the potential to aid in longitudinal cancer monitoring and in detection of low tumor burden and minimal residual disease. We aim to apply this approach to serial samples obtained through the LUCID study to investigate its application in treatment management. Citation Format: Katrin Heider, Jonathan C. Wan, Davina Gale, A