The new GLOBOCAN methods paper demonstrates global inequalities in data sources

Abstract

International Journal of Cancer (IJC) published at its web site paper “The GLOBOCAN 2022 cancer estimates: data sources, methods, and a snapshot of the cancer burden worldwide” by Adalberto Filho and co-workers from the International Agency of Cancer (IARC). The paper describes in detail how cancer incidence and mortality data on 36 cancer sites from 185 countries were collected. Different sources of data are illustrated in global maps. The detailed cancer-specific incidence and mortality data have been reported elsewhere.¹

The current IJC paper describes the way the incidence data were estimated for each country. Complete national rates were available for 55 countries (30%); 39 had regional rates that were applied to the whole country; for 52 countries, incidence was estimated based on mortality figures; in one country, total incidence data were partitioned to specific sites; for 38 countries lacking incidence data, the rates were extrapolated from neighbouring countries with registries. For mortality analysis, national rates were available for 93 countries (48%) in the WHO statistics (https://cdn.who.int/media/docs/default-source/gho-documents/global-healthestimates/ghe2021_cod_methods.pdf). For the remaining 93 countries, site-specific mortality was extrapolated from national incidence estimates using statistical models, with the fitted incidence to mortality (I:M) ratios derived from survival estimation (details are given in the supplement of the paper). Results in GLOBOCAN were expressed considering reliability of data with the help of uncertainty intervals, which are derived for standard errors adjusted for the degree of national coverage, timeliness and data quality.

Reliable incidence and mortality data on cancer are important for national and worldwide cancer control and prevention. Reliability may be assessed in terms of coverage (cases included of all cases) and diagnostic accuracy. The authors of the GLOBOCAN paper are well aware of the reliability issues as many of them are authors of the renowned quality opus of global cancer registers, Cancer Incidence in Five Continents, the last volume XII of which came out in 2023.²

GLOBOCAN used cancer registry data as available in 30% of countries, but for the remaining 70% of countries best estimates were used. A common quality indicator is the proportion cases in a cancer registries lacking any diagnostic data, called ‘death certificate only’ (DCO) cases. DCO rates were earlier high for many cancer registries, but according to Cancer Incidence, in Five Continents vol. XII DCOs are a few %, except for cancers of more difficult diagnosis, such as liver, pancreas and lung cancers, which are over 10% even in many European countries.²

In the GLOBOCAN study, mortality data for 48% of countries were derived from WHO statistics, which estimates quality of data for a half of the considered 120 countries as ‘high’ Moreover, there have been increasing concerns about the accuracy of mortality data for cancer as autopsy rates have declined in many developed countries.³ This is a problem for any internal cancers when patients die without prior medical records and the death registrar has to render cause of death only by inspection of the body. National data from Sweden on causes of deaths from 1999 to 2008 showed that for 9.6% of patients who had died of cancer, no hospital data with cancer diagnoses were found.⁴

The IARC's GLOBOCAN programme is an incentive in support of global efforts for cancer control and prevention, emphasizing population-based cancer registration and high-quality national vital statistics. An important tool for cancer prevention is the national cancer control plan, which should be periodically evaluated and revised.

KH is supported by the SALVAGE project, reg.no: CZ.02.01.01/00/22_008/0004644.