Cigarette smoking and lung cancer risk according to histologic type in Japanese men and women.

Although cigarette smoking is a well-known risk factor for lung cancer, histology-specific risk has not been fully clarified in Japan. This case-control study evaluated the associations between smoking and lung cancer risk according to sex and histologic type. From among patients aged 30 years and over admitted to a single hospital in Japan between 1997 and 2009, 1670 lung cancer cases and 5855 controls were selected. History of smoking, quantity and duration of smoking, and passive smoking from spouses were assessed using a self-administered questionnaire. Odds ratios (ORs) and 95% confidence intervals (CIs) for each exposure were estimated by unconditional logistic regression. Ever-smoking was significantly associated with a higher risk of squamous cell and small cell carcinoma. The OR for these two histologic types combined was larger in women (OR = 24.98, 95% CI: 13.50-46.23) than in men (OR = 9.43, 95% CI: 5.73-15.51). Analysis of the quantity and duration of smoking showed that the OR for each exposure level tended to be larger in women than in men. For adenocarcinoma, clear positive associations with quantity and duration-related factors were observed among men, and a significant positive association with passive smoking from spouses was found among non-smoking women (OR = 1.44, 95% CI: 1.06-1.95). These results suggest sex- and histologic type- differences in the association of smoking with lung cancer risk. Although smoking control should be continued to prevent lung cancers, further studies are required to better clarify differences in smoking-related lung cancer risk between the sexes and histologic types.