Passive smoking and lung cancer in Japanese non-smoking women: a prospective study.

Although smoking is a major cause of lung cancer, the proportion of lung cancer cases among Japanese women who never smoked is high. As the prevalence of smoking in Japan is relatively high in men but low in women, the development of lung cancer in non-smoking Japanese women may be significantly impacted by passive smoking. We conducted a population-based prospective study established in 1990 for Cohort I and in 1993 for Cohort II. The study population was defined as all residents aged 40-69 years at the baseline survey. 28,414 lifelong non-smoking women provided baseline information on exposure to tobacco smoke from their husband, at the workplace and during childhood. Over 13 years of follow-up, 109 women were newly diagnosed with lung cancer, of whom 82 developed adenocarcinoma. Compared with women married to never smokers, hazard ratio (HR) [95% confidence interval (CI)] for all lung cancer incidence in women who lived with a smoking husband was 1.34 (95% CI 0.81-2.21). An association was clearly identified for adenocarcinoma (HR 2.03, 95% CI 1.07-3.86), for which dose-response relationships were seen for both the intensity (p for trend = 0.02) and amount (p for trend = 0.03) of the husband's smoking. Passive smoking at the workplace also increased the risk of lung cancer (HR 1.32, 95% CI 0.85-2.04). Moreover, a higher risk of adenocarcinoma was seen for combined husband and workplace exposure (HR 1.93, 95% CI 0.88-4.23). These findings confirm that passive smoking is a risk factor for lung cancer, especially for adenocarcinoma among Japanese women.