Tobacco Smoking, Motor Exhaust Fumes, and General Air Pollution in Relation to Lung Cancer Incidence

age of cases is diagnosis made early enough for surgery to be curative. The survey results here presented represent a limited effort at a separate evaluation of the major factors most closely asso ciated with the disease incidence and indicate the likelihood of a contributing role for motor exhaust fumes. The finger of suspicion has now been pointed at three types of pollution: cigarette smoke, motor exhaust fumes, and general urban air pollution. Certain occupational dusts and fumes have been shown to be closely associated with lung cancer in exposed workers, but the total of all such occu pational cancers is insignificant amid the wide spread prevalence of the disease today. On the other hand, cigarette smokers seem definitely more prone than do nonsmokers to develop this type of cancer; and its over-all prevalence among indus trialized urban populations—more exposed to motor exhaust fumes and general urban air pollu tion—is fourfold higher than among rural resi dents. It is most unfortunate that many propo nents of tobacco smoking etiology have disregard ed the possibility that all factors work in synergy to pyramid the disease incidence in areas of at mospheric pollution and in the more exposed sex (males being more exposed to all factors). In reporting our 1946 studies (14, 16) showing lung cancer to be twice as prevalent among men living in polluted industrialized areas as in the clean suburbs of Chicago and Cincinnati, we re marked: "One would be inclined to look elsewhere