Cigarette smoking and subsequent risk of lung cancer by histologic type in middle‐aged Japanese men and women: The JPHC study

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Abstract
In order to update the findings of relative risk associated with cigarette smoking for lung cancer by histologic type in Japan, the data from a population-based cohort study of 91,738 men and women were analyzed. During 1990–1999, 422 lung cancer incident cases were identified. The relative risk for all incident cases associated with current smokers versus non-smokers was 4.5 [95% confidence interval (CI): 3.0–6.8] and 4.2 (95% CI: 2.4–7.2), for men and women, respectively. When divided by histologic type, relative risk for squamous cell carcinoma and small cell carcinoma was 12.7 (95% CI: 4.7–34.7) and 17.5 (95% CI: 4.9–62.1), while for adenocarcinoma it was 2.8 (95% CI: 1.6–4.9) and 2.0 (95% CI: 0.8–5.0) for men and women, respectively. We confirmed that the lung cancer risk in men rose with increasing cigarette smoking, especially the duration of smoking among current smokers and decreased after the cessation of smoking among former smokers. Unlike the US or European countries, the relative risk did not increase in this updated study, compared with previous studies in 1960s to 1990s in Japan either for all incident cases or for specific histologic types and the magnitude of relative risks was substantially lower than that observed in the US or European countries, especially for adenocarcinoma.