IMPORTANCE The inability to obtain a pathological diagnosis in a certain proportion of patients with clinically diagnosed advanced lung cancer impedes precision treatment in clinical practice. OBJECTIVE To evaluate the clinical outcome of first-line icotinib in patients with clinically diagnosed advanced lung cancer with unknown pathological status and positive epidermal growth factor receptor (EGFR)-sensitizing variants assessed by circulating tumor DNA (ctDNA). DESIGN, SETTING, AND PARTICIPANTS The Efficiency of Icotinib in Plasma ctDNA EGFR Mutation-Positive Patients Diagnosed With Lung Cancer (CHALLENGE) trial is a prospective, multicentered, open-label, single-arm phase 2 nonrandomized clinical trial conducted between July 1, 2017, and July 31, 2019. Patients with systemic treatment-naive, clinically diagnosed advanced peripheral lung cancer, unknown pathological status, and positive pretreatment plasma EGFR-sensitizing variants were eligible. A total of 391 potentially eligible Chinese patients from 19 centers in China were screened for ctDNA EGFR variants by 3 independent detection platforms (Super amplification refractory mutation system [SuperARMS] polymerase chain reaction, droplet digital polymerase chain reaction, and next-generation sequencing), and those with EGFR variants tested by any platform were included. Analyses were conducted from September 9 to December 31, 2021. INTERVENTIONS Enrolled patients were treated with oral icotinib tablets (125mg 3 times daily) until disease progression, death, or treatment discontinuation due to various reasons, such as toxic effects and withdrawing consent. MAIN OUTCOMES AND MEASURES The primary end pointwas objective response rate (ORR). The secondary end points included progression-free survival (PFS), overall survival (OS), disease control rate (DCR), and the concordance among the 3 detection platforms. RESULTS Of 116 included patients, 76 (65.5%) were female, and the median (range) age was 64 (37-85) years. The median (IQR) follow-up duration was 36.3 (30.2-40.7) months. The ORR was 52.6%(95% CI, 43.1%-61.9%). The median PFS and OS were 10.3 months (95% CI, 8.3-12.2) and 23.2 months (95% CI, 17.7-28.0), respectively, and the DCR was 84.5%(95% CI, 76.6%-90.5%). The concordance rate among the 3 detection platforms was 80.1% (313 of 391), and the clinical outcomes in patients identified as positive by any platform were comparable. CONCLUSIONS AND RELEVANCE This prospective phase 2 nonrandomized clinical trial suggests that for patients with clinically diagnosed advanced lung cancer with unknown pathological status, ctDNA-based EGFR genotyping could help decision-making in particular clinical situations, while still warranting future larger-scaled real-world exploration.