Early detection of pre-malignant lesions in a KRASG12D-driven mouse lung cancer model by monitoring circulating free DNA

Lung cancer is the leading cause of cancer-related death. Two-thirds of cases are diagnosed at an advanced stage that is refractory to curative treatment. Therefore, strategies for the early detection of lung cancer are urgently sought. Total circulating free DNA (cfDNA) and tumour-derived circulating tumour DNA (ctDNA) are emerging as important biomarkers within a 'liquid biopsy' for monitoring human disease progression and response to therapy. Owing to the late clinical diagnosis of lung adenocarcinoma, the potential for cfDNA and ctDNA as early detection biomarkers remains unexplored. Here, using a Cre-regulated genetically engineered mouse model of lung adenocarcinoma development, driven by Kras(G12D) (the Kras(LSL-G12D) mouse), we serially tracked the release of cfDNA/ctDNA and compared this with tumour burden as determined by microcomputed tomography (CT). To monitor ctDNA, a droplet digital PCR assay was developed to permit discrimination of the Kras(Lox-G12D) allele from the Kras(LSL-G12D) and Kras(WT) alleles. We show that micro-CT correlates with endpoint histology and is able to detect premalignant tumours with a combined volume larger than 7 mm(3). Changes in cfDNA/ctDNA levels correlate with micro-CT measurements in longitudinal sampling and are able to monitor the emergence of lesions before the adenoma-adenocarcinoma transition. Potentially, this work has implications for the early detection of human lung adenocarcinoma using ctDNA/cfDNA profiling.