Noninvasive identification of emergent mutations following cytotoxic therapy for lung cancer

8533 Background: Lung cancer is the leading cause of cancer death world-wide, and chemotherapy and radiation remain backbones of therapy for patients with locoregionally advanced and metastatic disease. However, the genetic mechanisms that mediate resistance to chemotherapy and radiation are largely unclear due to a lack of available tissue at the time of relapse. We hypothesized that circulating tumor DNA (ctDNA) analysis could identify emergent mutations after chemotherapy and radiation that may lead to treatment resistance. Methods: To identify emergent mutations at the time of progression following an initial response to chemotherapy and/or radiation therapy for lung cancer, we utilized CAncer Personalized Profiling by deep Sequencing (CAPP-Seq) to analyze plasma samples and matched leukocytes collected pre-treatment and at the time of relapse. We analyzed a targeted panel enriched for lung cancer drivers and recurrently mutated genes for 27 patients treated with chemoradiation therapy for locoregionally advanced lung cancer. In addition, we performed ultra-deep whole exome sequencing ( > 2000X deduped depth) of pre-treatment and relapse cell-free DNA for 5 patients treated with combination chemotherapy for metastatic lung cancer. Functional enrichment analysis was performed on emergent mutation gene lists to identify significantly enriched pathways. Results: We identified emergent variants in 6 out of 27 patients using targeted sequencing after chemoradiation therapy. Emergent mutations after chemoradiation were enriched for plasma membrane adhesion molecules such as PCDH17, PCDH10, and FAT3 (adjusted P = 0.03). Using ultra-deep whole exome sequencing, we observed emergent mutations in 3 out of 5 patients treated with combination chemotherapy. After combination chemotherapy, there was a trend towards enrichment in mutations in ATP-binding cassette transporters, including ABCA13 and ABCB4 (adjusted P = 0.057). Notably, there were no recurrent emergent mutations within our cohort. Conclusions: Our results suggest that ultra-deep whole exome sequencing can non-invasively identify emergent mutations at the time of progression. Resistance to cytotoxic therapy is likely multi-factorial and analysis in expanded cohorts will be helpful to identify recurrently mutated pathways that may contribute to disease progression after an initial response to therapy.