Global perspective of tobacco habits and lung cancer: a lesson for third world countries.

Over the past 50 years, a dominant role of tobacco smoking in lung cancer causation has been demonstrated. Almost three-quarters of the lung cancer cases can be attributed to tobacco smoking. The global variation in lung cancer incidence is thought to be directly proportional to the smoking habits prevalent in that part of the world. Lung cancer shows a greater upward trend in incidence in the USA, in central and Eastern Europe than ever before, especially in females. Japan too has recorded a 10-fold increase in incidence in both sexes since 1975. In India the problem is further compounded by absence of authentic data on time trend. The recent trend of available data suggests a more or less linear trend. At present lung cancer ranks among the top three killers in men in almost every metropolis in India. The highest incidence rate has been recorded in Bombay (14.6/ 100,000) and the lowest in Barshi (2.0/100,000). How much of these can be attributed to smoking cannot be commented on as no case-control or cohort studies have ever been undertaken in India. The situation is more alarming in other developing countries, where there is no authentic data on tobacco use or lung cancer incidences. The relationship between tobacco and cancer is both simple and complex. The majority of the cancer patients are smokers, while the cancer incidence is not proportional among smokers. To explain this, various factors such as type of smoke, duration of smoke, amount of carcinogens, presence of activation and metabolism pathways, and lately genetic environment interaction, have been put forward. It appears that the relationship is more complex than at first thought. In developing countries, it is further compounded by lack of data on usage and dependence of the economies of these countries on tobacco. The situation is alarming, with ever-increasing incidence among women and non-smokers exposed to smoke (passive smokers). Tobacco use has already become an epidemic.