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It had long been suspected by some that cigarettes might be carcinogenic, but it was only in the 1930s, when physicians began to encounter cases of lung cancer with increased frequency, that the issue received more significant attention. As early as 1932, Dr. William McNally of Rush Medical College suggested that cigarette smoking was an important factor in the higher rates of lung cancer. In 1938, in an article in the Science News Letter, Drs. Alton Ochsner and Michael DeBakey of New Orleans wrote: "More persons are dying of cancer of the lungs than ever before, probably because more persons are smoking and inhaling tobacco smoke than ever before." Ochsner continued to make this case throughout the 1940s, but he was dismissed by many of his colleagues as an antismoking enthusiast since he forbade his own staff from smoking.

Not everyone accepted the premise that the rise in the incidence of lung cancer was linked to cigarette smoking. Many physicians and scientists were skeptical about the epidemiological evidence. A statistical correlation between an increase in cigarette smoking and an increase in lung cancer does not prove that there is a causal connection. A prominent physician, Evarts Graham, who had been one of Ochsner's teachers, noted, "Yes, there is a parallel between the sale of cigarettes and the incidence of cancer of the lung but there is also a parallel between the sale of nylon stockings and cancer of the lung." Graham eventually did become more convinced of the connection between smoking and lung cancer.

Critics of the view that lung cancer was linked to smoking argued that other factors, such as increasing atmospheric pollution from automobile exhausts, might also explain the rise in the incidence of the disease. Some physicians even argued that the incidence of lung cancer only a appeared to be increasing because better diagnostic tools were making it easier to identify.

In 1950, Wynder and the above-mentioned Graham (in this country) and Doll and Hill (in England) published preliminary reports of independent studies showing an association between smoking cigarettes and lung cancer. The Americans would only cautiously state that extensive and prolonged smoking, especially of cigarettes, seemed to be an important factor in the inducement of lung cancer. The British researchers asserted somewhat more definitely that smoking was an important factor in the production of lung cancer. They admitted, however, that other factors could also cause the disease.

Although these were careful studies involving hundreds of patients, the research did not convince everyone that there was indeed a causal connection between smoking and lung cancer. The studies were criticized, for example, because they were retrospective and hence relied heavily on the recollections of patients. Even Graham himself did not quit smoking, although he cut back to a pack a day in 1953. Unfortunately, he died of lung cancer four years later.

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