Only three strategies are available for controlling cancer, prevention, screening and treatment. Lung cancer causes more deaths than any other type of cancer. A major cause of the disease is (51) known there is no good evidence that screening is of much help and treatment fails in about 90 per cent of all cases. At present, therefore, the main strategy must be (52) . This may not always be true, of course, as for some other types Of cancer, research (53) the past few decades has produced (or suggested) some important progress in prevention, screening or treatment. (54) , however, we consider not what research may one day offer but what today's knowledge could already deliver that is not being delivered, then the most practicable and cost-effective opportunities for avoiding premature death from cancer, especially lung cancer, probably involve neither screening nor improved (55) , but prevention. This conclusion does not depend on the unrealistic assumption that we can (56) tobacco. It merely assumes that we can reduce cigarette sales appreciably by raising prices or by (57) the type of education that already appears to have had a (58) effect on cigarette consumption by white-collar workers, and that we can substantially reduce the amount of tar delivered per cigarette. The practicability of preventing cancer by such measures applies not only in those countries, (59) the US, where, because cigarette smoking has been common for decades, 25～30 per cent of all cancer deaths now involve lung cancer, but also in those where it has become (60) only recently. In China, for example, lung cancer (61) accounts for only about 510 per cent of all cancer deaths. This is because it may take as much as half a century (62) the rise in smoking to increase the incidence of lung cancer. Countries where cigarette smoking is only now becoming widespread can expect enormous increases in lung cancer during the 1990s or early in the next century, (63) prompt effective action is taken against the habit--indeed., such increases are already plainly evident in parts of (64) . There are four reasons why the prevention of lung cancer is of such overwhelming importance: first, the disease is extremely common, causing more deaths than any other type of cancer now does secondly, it is generally incurable thirdly, effective, practicable measures to reduce its incidence are already reliably known and, finally, (65) tobacco consumption will also have a substantial impact on many other diseases. 51.