Daisuke Nishizaki, Allison Law, Bailiang Li, Charles W. Abbott, Yi Chen, Suzanna Lee, Rachel Marty Pyke, Kathleen C. Keough, Gregory A. Daniels, Kay T. Yeung, S. Boyle, R. Chen, Shumei Kato
Circulating tumor DNA (ctDNA)-based response assessment is appealing but limited by conventional analytical thresholds. We utilized a whole genome sequencing based, tumor-informed ultrasensitive ctDNA assay which tracked ~1800 somatic mutations to analyze 227 longitudinal plasma samples from 39 patients with advanced/metastatic cancers receiving immune checkpoint inhibitors (ICIs). ctDNA was detected from 2.0-239,315 PPM (median limit of detection: 1.77 PPM), with 33% of positive detections below 100 PPM. Early molecular response, defined as >50% ctDNA reduction or sustained ctDNA negativity from baseline to first follow-up, strongly predicted improved progression-free survival (PFS) (hazard ratio (HR) = 0.09, 95% CI: 0.02-0.39, p = 0.001) and was independently prognostic of PFS. Molecular complete response (mCR), defined as any ctDNA clearance, predicted overall survival and PFS, with 1-year PFS of 87% in mCR patients versus 16% in non-mCR patients (HR = 0.14, 95% CI: 0.04-0.50, p = 0.003). The high-sensitivity ctDNA monitoring may enable precise, real-time evaluation of ICI response to guide clinical decision-making.