Cigarette smoking causes lung cancer.(3) Lung cancer was the first major disease to be causally linked to cigarette smoking. The history of this research is discussed briefly in this book's introduction.
Lung cancer is the leading cause of cancer death in Australian men, and the third most common cause of cancer death in women (ranking behind breast and colorectal cancers).(5)
The risk of developing lung cancer is dose-response related: longer duration and heavier consumption patterns of smoking increase the likelihood of developing the disease. For example, a child who starts smoking aged 14 years or less is five times more likely to die of lung cancer than a person who starts aged 24 or more years, and 15 times more likely to die of lung cancer compared to someone who never smokes.(18)
Overall, smokers are ten times more likely to die from lung cancer than are non-smokers, and heavy smokers are 15 to 25 times more at risk than non-smokers.(3) The average Australian male smoker has an approximately one in ten chance of dying from lung cancer.(19) Eighty-four percent of lung cancer in men can be attributed to smoking, and 77% in women.(4)
Researchers in America have identified the first molecular evidence linking a specific compound in cigarette smoke directly to lung cancer. The study shows that benzo(a)pyrene in the tar damages the p53 gene, a gene which suppresses tumor development. A damaged p53 gene is found in about 60% of lung cancers.(19a)
Because lung cancer due to smoking usually takes 20 or more years to develop and tobacco usage is the major causative factor, lung cancer patterns in the community are an important indicator of the smoking patterns of earlier decades. Figure 3.2(20,21) shows that early this century, lung cancer was a comparatively rare disease. Rates began to increase in men during the 1930s and 1940s, reflecting a large uptake of smoking among men from around 1910 through to the 1920s. This is consistent with what is known from other sources: that tailor-made (rather than roll-your-own) cigarettes became common at around the time of the First World War, and that tobacco was freely supplied to the armed forces.(22 )Men's lung cancer mortality rates peaked in the early 1980s, and are now in a downturn, reflecting declining smoking rates over the past three decades.(21)
In the earlier part of this century few Australian women smoked, probably due to the influences of society. They took up smoking in perceptible numbers in the 1920s, and numbers increased during the following decades.(22) Reflecting this trend, the upswing in lung cancer mortality among women became more marked during the 1960s, increasing by 50%, and has continued to increase overall, although the rate of increase has begun to slow down.(21)
Men's death rates still far exceed those of women. This is because men began smoking in large numbers prior to women, and have always had a higher prevalence of smoking. Moreover, men tend to smoke more heavily than women, to choose cigarettes with a higher tar content, and to report longer duration of smoking than women,(23) probably reflecting an earlier age of uptake. Of the known factors which influence lung cancer risk, duration of smoking, and especially the role of smoking early in life, is the most significant.(24) Amount smoked per day is also important, but less so than early onset and duration.(24) Tar content is also a contributory factor, but decreases in average tar content in Australian cigarettes over the past twenty years (see Chapter 5, Section 3) suggest that this will be a less important influence in future disease trends.
The slowing in disease rates among women is more likely to be due to less hazardous smoking behaviour among women than any decrement in smoking prevalence, women's smoking rates overall having remained stable compared to those of men(21) (see Chapter 1, Section 1). However it is also worth noting that as female uptake of smoking is now occurring at a far earlier age than in previous decades, duration of smoking among women can be expected to extend.(25) This will contribute to future disease rates remaining high. See also Chapters 1 and 2.
It had been predicted that in the early 1990s lung cancer could overtake breast cancer as the leading cause of cancer death in women.(26) Although this has occurred among women in the United States(27) and in Glasgow, Scotland,(28) it has not done so among Australian women, and will not happen if the rate of increase of lung cancer deaths continues to decline among women (Figure 3.3).
Adult female smoking rates now appear to be falling,(29) and average sales weighted tar content of Australian cigarettes declined by 35% between 1969 and 1981 (see Chapter 5, Section 3) and continues to do so.(30) These factors are probably responsible for the reduction in the rate of increase in lung cancer mortality rates that has already been observed.(21)
Providing these trends do not change and there is no further reduction in the age of onset of smoking, which would tend to increase lung cancer death rates, a continuing decline in the rate of increase in female lung cancer rates can be expected. Although evidence from schoolchildren's smoking surveys between 1984-1990,(32,33,34) has suggested that the efforts to reduce smoking in this group have been successful, the latest survey (1993) is showing results contrary to the previous trends.(35) Future surveys will determine whether this represents an aberration or a significant alteration in patterns (see Chapter 1, Section 4).
As already noted, Australian female smoking behaviour is converging with that of males. Trends in male lung cancer death rates may therefore provide some guide to future disease trends in Australian women.
On this basis it is predicted that Australian female lung cancer death rates will peak at no higher than 14 cases per 100,000 by 1999, and decline thereafter. With female breast cancer death rates having been relatively static at around 20 cases per 100,000 for most of this century, it is improbable that lung cancer will ever overtake breast cancer as the leading cause of cancer death in Australian women, unless there is a dramatic downturn in breast cancer death rates.
Table 3.1 shows that there has been a rise in the death rate from lung cancer, concordant with consumption patterns of earlier decades.