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Interaction among lung cancer risk factors in a case-control study Wang, S.Y., Hu, Y.L., Chi, G.B., Li, X., Wu, Y.L., Chen, Y., and Dai, W.C. Department of Epidemiology, Medical College, Jinan University, Guangzhou 510632, China A case-control study investigating potential interactions among risk factors of primary lung cancer was carried out in Guangdong, China from 1991 to 1993. The study included 390 matched pairs. Study subjects were inpatients with primary lung cancer (age 32- 78), consisting of 171 cases of squamous cell cancer (L.S.), 138 cases of adenocarcinoma (L.A.), and 81 cases of other pathological type (L.S. : L.A. = 1:0.8). Squamous cell cancer accounted for the majority (51.55%) of the 291 male cases (L.S. : L.A. = 1:0.5). Primary lung adenocarcinoma made up the majority (57.57%) of the 99 female cases (L.S. : L.A. = 1:2.7). Single factor conditional logistic regression analysis showed that the occurrence of lung cancer was closely associated with history of chronic bronchitis, emphysema, pulmonary tuberculosis and other pulmonary diseases (OR=2.9-3.6, x =13. 52-37. 55, p<0.01). Other risk factors were smoking, passive smoking from the spouse or in the workplace, and family history of tumour (OR=2.7-3.6, x =8.53- 33. 15, p<0.o1). Occupation as a driver, taking oral contra- ceptives, frequent intake of pickles or salted fish, and bad ventilation in kitchen were possible lung cancer risk factors

(OR=1.3-3.0, x =4.78-5.0, p<0.05). Further multiple conditional logistic regression analysis suggested that history of chronic bronchitis, emphysema, pulmonary tuberculosis, smoking, family history of tumour, passive smoking from spouse or in the workplace, and frequent intake of pickles were independent lung cancer risk factors (OR=1.7-3.5). To investigate the interaction between the risk factors history of chronic bronchitis, emphysema, pulmonary tuberculosis, smoking and passive smoking, a log-linear model analysis was performed. The result revealed that there was significant interaction between two factors in a one-stage analysis. Although the interaction existed between chronic bronchitis and tuberculosis, chronic bronchitis and smoking or passive smoking, tuberculosis and passive smoking, it did not attain the level of significance among three or more factors (including the principal effect of lung cancer) in a two- stage analysis (x=1.31-2.27, p>0.13). The interaction of the former was not affected by the effects of the latter. - 2 -