Reexamining Rates of Decline in Lung Cancer Risk after Smoking Cessation. A Meta-analysis

Rationale: Prior studies have questioned whether prevailing eligibility criteria for lung cancer screening are sufficiently inclusive of former smokers who remain at elevated risk of disease outside current screening windows.Objectives: To characterize the percentage of the reducible relative risk (RR) remaining for lung cancer as a function of years since quitting (YSQ).Methods: MEDLINE and PubMed were searched from January 2011 to May 2018; key search terms included "smoking" and "cancer." Current smoker RRs were extracted to represent former smokers at 0 YSQ; data were transformed assuming a lognormal distribution.Results: The main review included 49 prospective cohorts across 18 studies comprising a total of 139 RRs from 20 countries and territories. At 1 year since quitting, the percentage of reducible RR remaining for lung cancer was 81.4% (64.1-98.2%). At 5 YSQ, the percentage of reducible RR remaining was 57.2% (45.7-67.3%); at 10 years, it was 36.9% (28.3-47.9%); at 15 years, it was 26.7% (20.2-34.3%); and at 20 years, it was 19.7% (13.3-26.4%). If eligibility criteria in the United States were broadened to screen former smokers at up to 20 YSQ, we estimate an additional 4.2 (3.9-4.5) million former smokers between 55 and 80 years of age would be eligible for lung cancer screening.Conclusions: At the critical screening threshold of 15 YSQ, the percentage of excess risk for lung cancer remains high and only marginally declines at time points afterward, excluding millions of former smokers who remain at elevated risk of malignancy. A risk-based algorithm for lung cancer screening that deemphasizes time after cessation as a key screening determinant would more likely capture these former smokers who remain at elevated risk of malignancy.