Global cancer mortality rose from 6 million in 19901 to 7 million in 2000.2 Aging of the world's population is a major factor contributing to the increase in cancer mortality because the incidence of most cancers increases with age. This demographic change is coupled with an epidemiologic shift, in which age-specific mortality has increased for some cancers (e.g., lung and breast) and decreased for others (e.g., stomach and cervix in many industrialized countries). This epidemiologic shift is in turn driven by changes in risk factors for cancers of different sites, including diet and the environment, infectious agents (e.g., for cervix uteri, liver and stomach cancers), behavioral risks such as alcohol and tobacco use and reproductive risks and behaviors. Tobacco smoking is currently the most widespread source of exposure to known carcinogens in the world and is causally associated with at least 15 types of cancer, as summarized in a review by the IARC and the 2004 report of the U.S. surgeon general.3, 4, 5, 6
Recent estimates of global cancer mortality attributable to smoking were based on cancers of multiple sites combined.7 These estimates are important for motivating global tobacco-control efforts such as the FCTC. Combined estimates do not, however, address regional differences in the background risks of specific cancer sites. This limitation arises because smoking affects cancer incidence and mortality in combination with other behavioral and environmental factors, all with important population-specific dynamics and potentially different biologic mechanisms. For example, coal is used for household heating and/or cooking in many regions of China8, 9 and has given rise to high background mortality from lung cancer, which is magnified by smoking.10 Fuel use patterns in China are, however, changing, with wealthier coastal communities shifting from coal to cleaner fuels (e.g., natural gas) and rural inland communities switching from wood to coal to avoid deforestation.9 Chewing betel-quid with tobacco, common in many parts of southern Asia, is a risk factor for oral cancer in combination with smoking and has been affected by changing social norms.11, 12, 13, 14 Alcohol consumption, an important risk factor for oral, esophageal and liver cancers, is currently increasing in some developing countries.15 Cancers with infectious risk factors also exhibit population-specific dynamics, ranging from a consistent decline in stomach cancer in many countries during much of the 20th century to an increase in cervix uteri cancer in some developing regions (e.g., sub-Saharan Africa).
Addressing the large and increasing GBD from cancers therefore requires an understanding of the role of smoking in combination with other risk factors. Data for multirisk factor models are extremely rare, especially in developing countries. In this report, we use 2 unique data sources, the American Cancer Society CPS-II as well as the WHO and the IARC cancer mortality databases, to estimate site-specific cancer mortality caused by smoking in the year 2000 for 8 clusters of site-specific cancers and 14 epidemiologic subregions. Estimates include cervix uteri, liver and stomach cancers, which have been identified as causally related to smoking in the recent IARC review and the 2004 report of the U.S. surgeon general.3, 4, 5 This report also provides estimates of site-specific cancer mortality for other cancers caused by smoking in different world regions, thus updating a similar attempt made in 1985 based on cancer incidence.16 New estimates are important because smoking increased in most developing countries over the last quarter of the 20th century, with an estimated 930 million of the world's 1.1 billion smokers currently living in the developing world.17, 18
A second contribution of this report is the use of RRs that are systematically and consistently adjusted for potential confounding covariates such as alcohol, diet and occupational exposures. Previous estimates of smoking-caused cancer mortality, whether in aggregate or site-specific estimates from 1985,7, 16, 19 used hazard estimates with no or partial adjustments for major covariates. The use of unadjusted, multicancer hazards necessitated the use of arbitrary hazard correction factors to ensure that the risks of tobacco were not overestimated.7, 19 This increased uncertainty in the estimates of cancer mortality caused by smoking. By using a comparable measure of exposure and systematically adjusted hazards, the estimates presented here provide a consistent basis for assessing the consequences of smoking in different regions of the world for global cancer epidemiology, and for assessing how global and regional tobacco-control efforts, such as those initiated under the FCTC, may contribute to reducing smoking-caused cancer mortality.