Pack-year

A pack-year multiplies the number of packs smoked a day by the number of years of smoking, taking a pack as twenty cigarettes. It is the measure every lung cancer screening rule is written in. The National Lung Screening Trial enrolled people with at least 30 pack-years who smoked or had stopped within 15 years; the US Preventive Services Task Force set its 2013 threshold at 30 pack-years and ages 55 to 80, and lowered it in 2021 to 20 pack-years and ages 50 to 80, a change that widened eligibility substantially and was aimed in part at groups whose lung cancer arises at lower cumulative exposure. England's programme does not use a pack-year cut-off at all: it feeds smoking duration and intensity, with age, body mass index, education, family history and lung disease, into a risk model and screens above a predicted-risk threshold. The unit has a known weakness: it treats twenty a day for thirty years and sixty a day for ten as equivalent, when duration raises lung cancer risk more steeply than intensity does.