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 16.2,(1,69) shows that lung cancer in men began to increase during the 1930s and 1940s, which would reflect a large uptake of smoking among men from around 1910 through to the 1920s. In the earlier part of this century few Australian women smoked. They took up smoking in perceptible numbers in the 1920s, and numbers increased substantially during the following decades.(3) 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.(1)
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,(70) 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.(71) Amount smoked per day is also important, but less so than early onset and duration.(71) Tar content is also a contributory factor, but decreases in average tar content in Australian cigarettes over the past 20 years (see Chapter 5, Section 3) suggest that this will be less important influence in future disease trends.
The slowing in lung cancer death rates among women since 1975-1979 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.(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.(2) 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.(72) Although this has occurred among women in the United States(73) and in Glasgow, Scotland,(74) 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 16.3).
Adult female smoking rates appear to be falling,(16) 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.(75) These factors are probably responsible for the reduction in the rate of increase in lung cancer mortality rates that has already been observed.(1)
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(21,22,23) 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.(24) Future surveys will determine whether this represents an aberration or a significant alteration in patterns (see Chapter 1).
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.
Around 5,063 Australian women died in 1992 from tobacco caused disease,(43) more than one death every two hours. Active smoking causes one in twelve deaths in Australian women, and one in five deaths in Australian men. Table 16.9 provides estimates of deaths by condition for 1992.