Background: Given the challenges of molecular profiling in patients with advanced lung cancer, this prospective study examines clinical outcomes and utility of liquid biopsy in treatment naive stage IV lung adenocarcinoma patients (Cohort 1) and in the setting of resistance to targeted therapy (Cohort 2; not reported here). Methods: This study is being conducted at 6 Canadian centres (NCT03576937) using Guardant 360 (G360), a validated cell-free DNA next-generation sequencing assay that identifies variants in 74 cancer-associated genes, including fusions and copy number gain. Cohort 1 (N = 150) includes patients with treatment-naïve advanced non-squamous lung carcinoma, ≤10 pack-year smoking history, and measurable disease. Patients received standard of care tumour tissue (TT) molecular profiling (EGFR, ALK +/- ROS1) and liquid biopsy (LB). The primary endpoint was response rate to first-line therapy (RECIST 1.1); secondary endpoints include incremental targetable alterations identified through G360 (EGFR, ALK, BRAF, ERBB2, KRAS (G12C), NTRK, MET (amplification, exon 14 skipping), RET, ROS1), turn-around time (TAT) and successful molecular profiling rates. Results: To date, 84 eligible patients with clinical data have been accrued to Cohort 1. Median age is 64 (range 23-91), 64% are female, 85% never smokers, 96% have adenocarcinoma. Actionable targets have been identified in 55% of patients using G360 (EGFR/ALK in 37%), 39% using standard TT profiling. Eight EGFR/ALK aberrations were identified in TT but not LB, while 6 were identified in LB but not TT. TT profiling for EGFR/ALK was unsuccessful in 8% of patients (insufficient tissue, failed biopsy). Fourteen patients (17%) had no ctDNA alterations detected by G360 (low disease burden vs. non-shedding). Of 75 patients receiving first-line treatment, 57% received targeted therapy, 28% chemotherapy combinations, 11% checkpoint inhibitors and 4% were observed. Treatment decisions were informed by G360 alone in 37% and by G360+TT results in 27% (by physician report). Among 46 evaluable patients, ORR was 54% (25/46). Using G360, ORR was 75% (15/20) in those with actionable alterations and 38.5% (10/26) in those without. Using TT, ORR was 67% (14/21) in those with actionable alterations and 44% (11/25) in those without. Mean TAT was 7.9 days (SD+/-1.7) for LB vs 19.9 days (SD+/- 9.8) for TT. Conclusions: Liquid biopsy using G360 identifies actionable targets beyond tissue profiling alone in newly diagnosed lung cancer patients, has faster TAT and yields similar outcomes with targeted and non-targeted therapy. Clinical trial information: NCT03576937.