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: I I I I I I I I I I RELATIONSHIP BETWEEN LIFESTYLE FACTORS AND LUNG CANCER IN HUMANS BASED ON TREND ANALYSIS OF LUNG CANCER INCIDENCE IN XUANWEI, CHINA Xu Chong-wang Tumor Prevention and Treatment Research Center of Xuanwei County, Yunnan, China Xuanwei County is an agricultural community located in northeast Yunnan Province of China. It occupies an area of 6,075 square kilometers and has a population of 1,220,000 (640,000 males and 580,000 females). Its major products are coal, hogs, and the well-known salt-cured, coal-smoked "Xuanwei ham." Historically, Xuanwei has always had a higher lung cancer death rate than any of the comparable agricultural counties. In 1973, the lung cancer death rate for Xuanwei residents was 26.23 (per 100,000; male: 27.95, female: 24.50). During the same period, the cancer death rate was 10.92 for the neighboring Fuyuan County, 11.62 for Kaifeng (Henan Province), 8.66 for Zhuanghe (Heilongjiang) and 8.12 for Lueyang (Shaanxi Province). Thus, Xuanwei's lung cancer death rate is 2-3 times higher than any of the other comparable areas. Although the male and female residents of Xuanwei differ greatly in their smoking habits -- more than 90% of the men are smokers while smokers among women are extremely rare -- little difference in lung cancer incidence for the two sexes is observed. The average male-female lung cancer ratio falls between 1.1:1 and 1:1. Xuanwei residents traditionally use coal-burning earthen stoves, without chimneys, for cooking, heating, and to smoke their ham products. The poor design of the stoves has been blamed for the severe indoor air pollution problems in Xuanwei. In 1977, for example, a 559 µg/100M° benzo(a)pyrene B(a)P level was found in a heavily polluted farm house. Average levels of 75.95 µg/100M° and 159.70 µg/100M' of B(a)P were reported in 1980 and 1983 in the peasants' homes. A test was conducted by placing groups of laboratory animals in coal-burning and wood-burning households and letting the animals breathe the ambient air containing coal- or wood-smoke. The results showed the occurrence of malignant tumors in the animals exposed to coal-smoke. Additionally, lung cancers were induced in mice injected with extracts from coal-smoke particulates. In 1976 some urgent measures to combat indoor smoke-and dust were implemented; these involved converting the existing earthen stoves, without chimneys, to draft-air furnaces with chimneys. In 1991 nearly 71.29% of Xuanwei's households had completed the conversion, which resulted in a general decrease of exposure to indoor air pollutants for the residents. In spite of these improvements, an upward trend in lung cancer death rate continues to be observed: the mortality rate was 26.23 (per 100,000) for 1973-75, 27.48 for 1984-86, and 28.43 for 1990-91. This suggests that indoor air pollution cannot be the only risk factor responsible for the high incidence of lung cancer in Xuanwei.