The epidemiology of lung cancer.

Lung cancer is the most frequent cancer worldwide, accounting for about 12% of all new cancer diagnoses in the two sexes combined. During the 1950s and 1960s clear evidence emerged that smoking was the cause of striking lung cancer increases. Risk of lung cancer increases approximately with the fourth power of duration of smoking and the square of the number of cigarettes smoked daily. Between 1990 and 1994, lung cancer mortality rates showed first decreases in the US and several European countries, including Italy, in men although not in women. Marked shifts are, however, taking place in the incidence of different histologic types. Adenocarcinoma, which had always been the predominant type in women and non-smokers, is increasingly associated with tobacco smoking. Since the 1950s steady rises in the incidence of adenocarcinoma of the lung have been observed in many developed countries. Increases are similar in the two sexes and have followed a clear cohort pattern, paralleling changes in smoking habits and cigarette design more than diagnostic advances. Low-yield filter cigarettes tend to be inhaled more deeply than high-yield cigarettes in order to satisfy a craving for nicotine. The peripheral part of the lung, where most adenocarcinomas arise, is thus exposed to a disproportionately higher amount of smoke carcinogens. The hazards of light and ultra-light cigarettes tend to be underestimated, whereas the only safe cigarette is the non-smoked one.