Tracking early lung cancer metastatic dissemination in TRACERx using ctDNA

Circulating tumour DNA (ctDNA) can detect and profile residual tumour cells persisting after curative intent therapy(1). Large patient cohorts incorporating longitudinal plasma sampling and extended follow-up are required to determine the role of ctDNA as a phylogenetic biomarker of relapse in early-stage non-small-cell lung cancer (NSCLC). Here, we developed ctDNA methods tracking a median of 200 mutations identified in resected NSCLC tissue across 1069 plasma samples collected from 197 patients enrolled in the TRACERx study(2). Lack of preoperative ctDNA detection distinguished biologically indolent lung adenocarcinoma with good clinical outcome. Postoperative plasma analyses were interpreted within the context of standard-of-care radiological surveillance and administration of cytotoxic adjuvant therapy. Landmark analyses of plasma samples collected within 120 days post-surgery revealed ctDNA detection in 25% of patients, including 49% of all patients who experienced clinical relapse; 3 to 6 monthly ctDNA surveillance identified impending disease relapse in an additional 20% of landmark negative patients. We developed a bioinformatic tool (ECLIPSE) for non-invasive tracking of subclonal architecture at low ctDNA levels. ECLIPSE identified patients with polyclonal metastatic dissemination, which was associated with poor clinical outcome. Through measuring subclone cancer cell fractions in preoperative plasma, we found subclones seeding future metastases were significantly more expanded compared to non-metastatic subclones. Our findings will support (neo)adjuvant trial advances and provide new insights into the process of metastatic dissemination using low ctDNA level liquid biopsy.