- Smoking History: Current or former (defined as subjects who have quit smoking for at least 3 months prior to Screening/Visit 1) cigarette smokers with a >10 pack-year smoking history. Number of pack years = (number of cigarettes per day/20) x number of years smoked (for example, 10 pack-years is equal to 20 cigarettes per day for 10 years, or 10 cigarettes per day for 20 years).