查看文章

Lung cancer is the leading cause of cancer mortality in the United States accounting for an estimated 28 percent of all cancer deaths in 1998, or a total of 160,100 deaths (1). Lung cancer is also the most common cause of cancer mortality worldwide (2). Although the majority of lung cancers can be attributed to cigarette smoking, particularly in Asian and middle eastern countries, a substantial percentage of lung cancer cases occurs among never smokers (3). For example, the proportion of female lung cancer cases who have never smoked is as high as 65 percent in China (4), 70 percent in Japan (5), and 94 percent in northern India (6). In the United States, typically 9-13 percent of female lung cancer cases are never smokers (7-11). In males, the patterns differ considerably. Among male lung cancer patients, the proportion of never smokers is about 2 percent in the United States (11-13), 3 percent in China (14), 9 percent in Japan (5), and 19 percent in northern India (6). Compared with the relation between smoking and lung cancer, very few studies have examined risk factors for lung cancer among nonsmokers. It is important to understand the patterns and etiology of lung cancer among nonsmokers for several reasons. First, Schneiderman et al.(15) have estimated US nonsmoking lung cancer death rates; if their estimates are valid, only colon and prostate cancer in men and colon and breast cancer in women exceed nonsmoking lung in annual cancer mortality. Second, while US lung cancer