Female sex and lung cancer risk in two large screening cohorts

Epidemiological studies have shown mixed results as to whether women are more susceptible to lung cancer than men. We studied 154,897 never-smokers and ever-smokers in the Prostate-Lung-Colon-Ovary (PLCO) trial and 53,452 heavy ≥30 pack-year smokers in National-Lung-Screening-Trial (NLST), 55-74 years of age. We calculated female to male lung cancer incidence rate ratios (IRR) using Poisson regression to adjust for established risk factors. In PLCO, women were more likely than men to be never smokers (56.2 % vs. 31.7 %, p < 0.01). Among ever smokers, women had fewer pack years than men (23 vs. 33 in PLCO, and 45 vs. 52 in NLST, p < 0.01). In adjusted analyses of PLCO, women had similar rates of lung cancer to men in the never-smoker group (IRR: 1.23, 95 %-confidence interval: 0.90-1.67), and the 1-15 (0.82, 0.59-1.14), 15-30 (0.95, 0.78-1.15), 30-45 (0.95, 0.80-1.11), 45-60 (0.94, 0.80-1.11), 60-75 (0.99, 0.81-1.19) and 75-100 (0.84, 0.67-1.06) pack-year groups. Lung cancer risk was lower among women in the 100+ pack year group (0.66, 0.48-0.90). In NLST, women were equally susceptible to lung cancer as men in all pack-year groups. There was no significant sex-race interaction (p > 0.05) in either trial, while there was a sex-age interaction (p = 0.02) in NLST. Our analysis of two large randomized cancer-screening trials with predominantly white participants shows that for never-smokers or ever-smokers aged >55 years, women are at similar risk of lung cancer compared to men. Consequently, lung cancer screening efforts, policies and campaigns, when addressing individuals of these demographics, should be equally focused on men and women.