- Current or former smokers with a >10 pack-year cigarette smoking history [number of pack years = (number of cigarettes per day / 20) X number of years smoked (e.g., 10 pack-years is equal to 20 cigarettes per day for 10 years, or 10 cigarettes per day for 20 years]. Former smokers are defined as those who have quit smoking for at least 3 months prior to the screening visit.