BACKGROUND-AIM:
While in Western countries smoking prevalences have generally declined for both sexes, sex-specific smoking patterns remain heterogeneous in many countries. In Spain, in women ages >55 smoking prevalence has been rising since 1991. This study analyses smoking prevalence projections for the Spanish population, focusing on sex and birth-cohort differences and potential impact in screening eligibility strategies.

METHODS:
We evaluated data from the Spanish National Health Surveys (ENSE) years 1987-2012 and the European Health Survey in Spain (EHSS), years 2009, 2014, 2017 and 2020 to construct detailed information on smoking behaviour in Spain through the Microsimulation Screening Analysis (MISCAN) Lung model. This includes age-specific smoking initiation and cessation probabilities by birth-cohort and sex. In addition, the effects of smoking on non-lung cancer mortality are incorporated. We included cohorts from 1940 to 1975 for this analysis. Using the MISCAN model, we reconstructed and projected smoking prevalence for current and former smokers until the year 2035, stratified by sex and birth-cohort.

RESULTS:
While overall current smoking prevalence is expected to decrease for both sexes, current smoking prevalence in women is expected to surpass that in men for the 1955-1969 birth cohorts in 2035 (7.6-17.7% versus 5.1-12.1%). Current smoking prevalence for women already surpassed that of men in the 1965-1969 birth-cohort in 2020 (27.8% versus 26.5%). However, among men, the youngest cohorts (1970-1974 and 1975-1979) are projected to have the highest prevalence of current smokers (12.3% and 12.4% respectively), compared to 9.7% and 3.9% in women. Regarding women former smokers, older cohorts (1940-1954) will remain stable. In contrast, prevalence in younger birth-cohorts (1955-1975) will grow to 30.9%-45.2% in 2035. In men, former smoking prevalence is projected to rise in all cohorts (1940-1975), particularly in the 1950-1954 (42.5% to 57.4%) and 1955-1959 cohorts (39.9% to 60.4%) by 2035.

CONCLUSIONS:
A change in smoking prevalence is projected for current and former smokers in the next 10 years in Spain. Women in several birth-cohorts (1950-1965) will experience a higher prevalence in current smokers than men. Since smoking prevalence is decreasing in both sexes, we project a bigger decrease in men than in women. Consequently, a higher percentage of men former smokers is projected for the older cohorts (1940-1955), whereas for women former smokers, a higher percentage is projected in the youngest cohorts (1970-1975). These changes in smoking patterns must be addressed, especially considering that former smokers could benefit more from a lung cancer screening programme than current smokers. Differences in selection criteria should be considered, since pack-year criteria exclude a high percentage of former smokers, compared to risk-prediction models.