IMPORTANCE Lung cancer screening has demonstrated survival benefits among heavy smokers, forming the basis of current age- and smoking intensity-based eligibility criteria. However, applicability of these criteria in Asia remains uncertain, where many cases occur outside current criteria, including among persons with no smoking history.

OBJECTIVE To evaluate the proportions, characteristics, and survival outcomes of Korean patients with lung cancer according to international screening eligibility.

DESIGN, SETTING, AND PARTICIPANTS This nationwide, population-based cohort study included individuals newly diagnosed with lung cancer in Korea between 2013 and 2018, prior to implementation of the national lung cancer screening program. Participants were followed up until December 31, 2021. Patients were classified as meeting the 2023 American Cancer Society screening eligibility criteria (aged 50-80 years with a smoking history of ≥20 pack-years [PY]) were compared with individuals with less than 20 PY, and persons with no smoking history within the same age range. Data were analyzed from August to December 2025.

EXPOSURES Age and smoking intensity in PY.

MAIN OUTCOMES AND MEASURES The primary outcome was all-cause mortality. Lung cancer-specific mortality was evaluated as a secondary outcome.

RESULTS Of 89 860 patients with lung cancer (mean [SD] age at diagnosis 67.8 [10.2]; 63 003 [70.1%] male), 31 804 (35.4%) met screening eligibility criteria, 39 627 (44.1%) had no smoking history, and 4232 (4.7%) were aged younger than 50 years. Among individuals aged 50 to 80 years, screening eligibility differed markedly by sex, with 31 277 men (56.8%) and 527 women (2.3%) meeting the screening criteria. Distant metastatic disease was present in 13 023 patients (40.9%) in the screening-eligible group, 5233 patients (41.1%) with less than 20 PY, and 12 192 patients (36.9%) with no smoking history. Compared with the screening-eligible group, risks of both all-cause and lung cancer-specific mortality were significantly lower among individuals with less than 20 PY of smoking (all-cause mortality: adjusted hazard ratio [aHR], 0.95; 95% CI, 0.93-0.98; lung cancer-specific mortality: adjusted subdistribution HR [aSHR], 0.96; 95% CI, 0.93-0.99) and individuals with no smoking history (all-cause mortality: aHR, 0.86; 95% CI, 0.84-0.88; lung cancer-specific mortality: aSHR, 0.86; 95% CI, 0.84-0.88) aged 50 to 80 years.

CONCLUSIONS AND RELEVANCE In this cohort study of Korean patients with lung cancer, international screening guidelines excluded 64.6% of patients, a substantial proportion of whom had no smoking history. Ineligible patients had lower mortality risk than screening-eligible patients. These findings suggest that population-specific strategies are needed to improve early detection among individuals not captured by current screening criteria.