The suspicion that cancer of the mouth is somehow associated with the use of tobacco goes as far back as 1739 AD. In the nineteenth century, several cases of cancer of the mouth were reported in which chewing of tobacco was incriminated.
A correlation between increase of cigarette smoking and the rising incidence of lung cancer was, for the first time, commented upon during the first quarter of the twentieth century, in the USA, Germany and Great Britain. It was, however, only in 1950’s that a cause-and-effect relationship could be shown to exist, with a fair certainty between excessive cigarette smoking and the development of lung cancer. This came about as a result of intensive clinical and epidemiological, as well as experimental studies the world over.
Clinical Studies: More than thirty such studies have been conducted so far in ten countries including Great Britain, USA, West Germany, Finland, France, Japan, the Netherlands, Norway and Switzerland. The British investigations, started in 1947 under Dr. Doll and Dr. Hill, drew the maximum attention. This inquiry covered 1465 lung cancer patients who were compared with an equally large group of carefully selected controls (those of same age and sex but not having cancer). The analysis of the data from this and other studies revealed the following facts:
1. Smokers run a greater risk of getting lung cancer.
2. This risk increases with the greater amount of tobacco consumed; heavy smokers (more than 25 cigarettes a day) run a much higher risk.
In another study carried out in Britain, a questionnaire as sent in 1951, to 60,000 doctors of or above the age of 35 years. Sufficient information was received from 40,000 of them to enable the investigators to classify the smokers according to the prevailing smoking habits at the time of enquiry. Upon the death of any of them, the necessary details as regards the causes of death were obtained and confirmed. The results obtained were as follows:
Lung cancer mortality increases consistenty and steeply with increased tobacco smoking. For heavy smokers (25 gm or more a day), the mortality is 24 times more compared to non-smokers, for moderate smokers (15-24 gm a day), it is 12 times more, and for mild smokers (1-14 gm a day), it is seven times more.
The American follow-up studies of Dr. Hammond and Dr. Horn, took into consideration the smoking habits of 187,766 male whites between the ages of 50 and 70 years belonging not only to large and small towns but also to rural areas. Their conclusions were:
Those who regularly smoke up to 20 cigarettes a day are about 25 times more prone to lung cancer than a non-smoker; this figure mounts to roughly 45 times for those who smoke between 20 and 40 cigarettes a day and reaches a multiple of approximately 90 for chain-smokers who smoke more than 40 cigarettes a day.
Besides the above studies, there are other interesting observations which indicate the cause-and-effect relationship between cigarette smoking and lung cancer.
1. In Iceland, the people smoked very little until after 1941, when they took to it because of the contacts offered by the American occupying troops. An analysis of the postmortem examinations performed between 1932 and 1938, revealed lung carcinoma to be a rare disease.
2. On post-mortem examination of 11,365 pairs of lungs of Bantu miners in South Africa who died between 1916 and 1949, lung cancer was found only in 6 cases, while it was found 114 times more among 8465 white miners. Bantu people scarcely smoked cigarettes, white population did.
3. A much higher death rate from lung cancer was found among European-born Jews in Israel in 1957, than among those born in Asia and Africa; in the latter countries, during the preceding decades, cigarettes were not so popular.
4. In a non-smoking, non-drinking community of the Seventh Day Adventists in the United States, between 1952 and 1956, only one case of lung cancer was observed, and if we take into consideration the general population, there should have been at least 10 to 11 cases of lung cancer.
5. Lung cancer has scarcely been seen among the Sikhs in India; they are, by their religion, forbidden to smoke or use tobacco in any form.
6. Examination of lungs of smokers dying from causes other than lung cancer has revealed a step-by-step change in the lung cells leading towards lung cancer.