International Lung Screen Trial (ILST)

* Inclusion Criteria: * Women or men age from 55 to 80. * Current or former smokers. A former smoker is defined as one who has stopped smoking for one or more years. * An estimated 6-year lung cancer risk of ≥1.51% based on the PLCOm2012 risk prediction model or ≥ 30 pack-years smoking history (pack-year is defined as number of pack of cigarettes smoked per day multiply by the number of years smoked. If a participant stopped smoking for 6 months or more and then restarted smoking again, the time will be subtracted from the total duration of smoking in 0.5 year increments) * ECOG performance status 0 or 1. * Capable of providing, informed consent for screening procedures (low dose spiral CT) * Exclusion Criteria * Clinical symptoms suspicious for lung cancer e.g. hemoptysis, chest pain, weight loss * Any medical condition, such as severe heart disease (e.g. unstable angina, chronic congestive heart failure), acute or chronic respiratory failure, home oxygen therapy, bleeding disorder, that in the opinion of the investigator could jeopardize the subject's safety during participation in the study or unlikely to benefit from screening due to shortened life-expectancy from the co-morbidities * Have been previously diagnosed with lung cancer * Have had other non-curatively treated cancer outside the lung. * Pregnancy * Pneumonia or bronchitis requiring antibiotic treatment within the last 12 weeks * Unwilling to have a spiral chest CT * Chest CT within 2 years * Does not fit into CT scanner table due to gross obesity * Cannot lie on CT scanning table on the back with arms over the head * Received chemotherapy or cytotoxic drugs within the last 6 months * Unwilling to sign a consent