Association Between Smoking and Incidence of Cancer

Summary

A population based study 1 identified lifelong smokers of <1 or 1-10 cigarettes per day (CPD) and evaluated risk of incident cancer among 238 525 cancer-free adults, aged 59-82. Relative to never smokers, current smokers who reported consistently smoking 1-10 CPD over their lifetime were 2.34 (95% CI 1.86 to 2.93) times more likely to develop smoking-related cancer. Current lifetime smokers of <1 CPD were 1.89 (95% CI 0.90 to 3.96) times more likely to develop tobacco-related cancer, although the association did not reach statistical significance. Associations were observed for lifelong smoking of ≤10 CPD with lung cancer (HR 9.65, 95% CI 6.93 to 13.43); bladder cancer (HR 2.22, 95% CI 1.22 to 4.05); and pancreatic cancer (HR 2.03, 95%CI 1.05 to 3.95). Among lifelong ≤10 CPD smokers, former smokers had lower risks of smoking-related cancer with longer time since cessation and longer smoking duration.

Another population based study 2 investigated the mortality associated with current and former use of cigars, pipes, and cigarettes (n=357 420). Exclusive current cigarette smokers (HR 1.98; 95% CI 1.93 to 2.02) and exclusive current cigar smokers (HR, 1.20; 95% CI 1.03 to 1.38) had higher all-cause mortality risks than never tobacco users. Exclusive current cigarette smokers (HR 4.06; 95% CI, 3.84 to 4.29), exclusive current cigar smokers (HR 1.61; 95% CI 1.11 to 2.32), and exclusive current pipe smokers (HR 1.58; 95% CI 1.05 to 2.38) had an elevated risk of dying from a tobacco-related cancer (including bladder, esophagus, larynx, lung, oral cavity, and pancreas). Among current nondaily cigarette users, statistically significant associations were observed with deaths from lung cancer (HR 6.24; 95% CI 5.17 to 7.54), oral cancer (HR 4.62; 95% CI 1.84 to11.58), and chronic obstructive pulmonary disease (HR 7.66; 95% CI 6.09 to 9.64) as well as for daily smokers.

An analysis 3 of data from Framingham Heart Study Original (n = 3905) and Offspring cohort (n = 5002) assessed lifetime smoking and lung cancer incidence. On follow-up (median = 28.7 years), 284 lung cancers were detected: incidence rates/1000 person-years in current, former, and never smokers were 1.97 (95% 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. Heavy former (vs never) smokers had elevated lung cancer risk at all years since quitting (<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). Heavy former (vs current) smokers had 39.1% lower lung cancer risk within 5 years since quitting. Among all former smokers, 40.8% of lung cancers occurred after more than 15 years since quitting.