Tindle HA, et al. - Researchers compared current, former, and never smokers and lung cancer risk by using multivariable-adjusted Cox proportional hazards regression models. Compared with continuing smokers, heavy former smokers exhibited a drop in lung cancer risk within five years since quitting (YSQ), but in comparison to never smokers, it continued to be more than threefold higher after 25 YSQ. They also reported the occurrence of four of ten lung cancers in former smokers with more 15 YSQ, beyond the screening window of the current guideline.

Methods

• Researchers used the Framingham Heart Study Original (n=3,905) and Offspring cohort (n=5,002) to select participants for whom they analyzed data for lifetime smoking and lung cancer incidence from 1954 to 1958 (Exam 4) and 1971 to 1975 (Exam 1), respectively, through 2013.
• Using multivariable-adjusted Cox proportional hazards regression models, they compared current, former, and never smokers and lung cancer risk.
• Every two years (Original) or four years (Offspring), smoking status and covariates were time-updated.
• They carried out primary analyses, which were restricted to heavy ever smokers with more than 21.3 pack-years; all ever smokers were included in additional analyses.

Results

• They detected 284 lung cancers on follow-up (median = 28.7 years); the estimated incidence rates/1,000 person-years in current, former, and never smokers were 1.97 (95% confidence interval [CI] = 1.66 to 2.33), 1.61 (95% CI = 1.34 to 1.93), and 0.26 (95% CI = 0.17 to 0.39), respectively.
• Findings demonstrated elevated lung cancer risk at all YSQ among heavy former (vs never) smokers (<5: hazard ratio [HR] = 12.12, 95% CI = 6.94 to 21.17; 5–9: HR = 11.77, 95% CI = 6.78 to 20.45; 10–14: HR = 7.81, 95% CI = 3.98 to 15.33; 15–24: HR = 5.88, 95% CI = 3.19–10.83; ≥ 25: HR = 3.85, 95% CI = 1.80 to 8.26).
• They observed 39.1% lower lung cancer risk within five YSQ among heavy former (vs current) smokers.
• Data showed that among all former smokers, 40.8% of lung cancers occurred after more than 15 YSQ.