Days from randomization to date when participant was last known to be free from lung cancer: Days until the date the participant was last known to be free of lung cancer.  This date comes from a participant study update form, except for ACRIN participants with cancer, where the cancer diagnosis date is used.Do not use this variable to calculate follow-up time for lung cancer incidence rates, Cox regressions, etc.  Instead, use fup_days for non-cases and candx_days for cases.