Estimating the world cancer burden: Globocan 2000

Abstract

Describing the distribution of disease between different populations and over time has been a highly successful way of devising hypotheses about causation and for quantifying the potential for preventive activities.1 Statistical data are also essential components of disease surveillance programs. These play a critical role in the development and implementation of health policy, through identification of health problems, decisions on priorities for preventive and curative programs and evaluation of outcomes of programs of prevention, early detection/screening and treatment in relation to resource inputs. Over the last 12 years, a series of estimates of the global burden of cancer have been published in the International Journal of Cancer.2-6 The methods have evolved and been refined, but basically they rely upon the best available data on cancer incidence and/or mortality at country level to build up the global picture. The results are more or less accurate for different countries, depending on the extent and accuracy of locally available data. This "data-based" approach is rather different from the modeling method used in other estimates.7-10 Essentially, these use sets of regression models, which predict cause-specific mortality rates of different populations from the corresponding all-cause mortality.11 The constants of the regression equations derive from datasets with different overall mortality rates (often including historic data from western countries). Cancer deaths are then subdivided into the different cancer types, according to the best available information on relative frequencies. GLOBOCAN 2000 updates the previously published data-based global estimates of incidence, mortality and prevalence to the year 2000.12 The data sources that have been used to build up the global estimates are as follows. Incidence, the number of new cases occurring, can be expressed as the annual number of cases (the volume of new patients presenting for treatment) or as a rate per 100,000 persons per year. Incidence data are produced by population-based cancer registries.13 Registries may cover national populations or, more often, certain regions. In developing countries in particular, coverage is often confined to the capital city and its environs. It was estimated that, in 1990, about 18% of the world population were covered by registries, 64% of developed countries and 5% of developing countries, although the situation is improving each year. The most recent volume of "Cancer Incidence in Five Continents" (CI5) contains comparable incidence information from 150 registries in 50 countries, primarily over the period 1988–1992.14 Survival statistics are also produced by cancer registries by the follow-up of registered cancer cases. Population-based figures are published by registries in many developed countries, for example, the SEER program covering 10% of the U.S. population15 and the EUROCARE II project, including 17 countries of Europe.16 Survival data from populations of China, the Philippines, Thailand, India and Cuba have been published by Sankaranarayanan et al.17 Mortality is the number of deaths occurring and the mortality rate the number of deaths per 100,000 persons per year. It is the product of incidence and fatality (the inverse of survival) of a given cancer. Mortality rates measure the average risk to the population of dying from a specific cancer, while fatality (1-survival) represents the probability that an individual with cancer will die from it. Mortality data are derived from vital registration systems, where the fact and "underlying" cause of death are certified, usually by a medical practitioner. Their great advantage is comprehensive coverage and availability. By 1990, about 42% of the world population was covered by vital registration systems producing mortality statistics on cancer. Not all are, however, of the same quality in all countries. National-level statistics are collated and made available by the World Health Organiztion (http://www-dep.iarc.fr/dataava/globocan/who.htm), although for some countries coverage of the population is manifestly incomplete (so that the so-called mortality rates produced are implausibly low) and in others, quality of cause of death information is poor. Frequency data, e.g., case series from hospitals and pathology laboratories, provide an indication of the relative importance of different cancers in a country or region in the absence of a population-based registry and mortality statistics. There are problems in extrapolating the results to the general population, since such series are subject to various forms of selection bias. Such data are generally published locally or in journal articles, although a few compendia are available.18, 19 Prevalence is the proportion of a population that has the disease at a given point in time.20 For many diseases (e.g., hypertension, diabetes), prevalence usefully describes the number of individuals requiring care. For ca