Understanding the global impact of primary brain tumors: The untapped potential of population-based cancer registries

See the article by Girardi et al. pp. 1765–1776

Population-based cancer registries are vital for cancer surveillance, research, and control. However, the practical utility of a registry for understanding the epidemiology of a particular cancer and informing public health decision making and resource allocation for that cancer is directly correlated with the completeness and accuracy of the data entered into it. Although cancer registries have improved significantly in recent years, there remains an overwhelming need for high-quality cancer incidence data from low- and middle-income countries.¹ Moreover, even among countries with more advanced health care systems and the infrastructure necessary for health data collection and maintenance, the quality of cancer registry data varies markedly.² These issues are especially pertinent for relatively rare tumors, such as those arising in the central nervous system (CNS),³ as an improved understanding of the incidence, distribution, and outcomes associated with these uncommon tumors is critically dependent on widespread, systematic, and accurate data collection from individual patients.

The study by Girardi and colleagues in this issue⁴ utilized the CONCORD database, a global cancer surveillance program that collates patient-level tumor data from over 300 population-based cancer registries.⁵ The authors analyzed the histologies of the nearly 700 000 malignant and benign primary brain tumors reported in these registries over a 14-year period, including data from 59 countries spanning 5 continents.⁴ Importantly, these data included brain tumors from all age groups, providing a full picture of cancer registration practices across both adult and pediatric brain tumor populations. While there are numerous informative and potentially actionable findings from this study, perhaps the most remarkable is the extreme variation in the histology distribution of primary brain tumors reported across the world. Key examples include the proportion of childhood brain tumors classified as low-grade astrocytoma, which ranged from 6% to 50% depending on the country, and the proportion of adult brain tumors classified as glioblastoma, which ranged from 9% to 69%. Equally concerning is that the proportion of tumors classified as having “unspecified histology” was alarmingly high in certain countries, with some such as China reporting higher proportions of tumors being classified as “unspecified” than those being classified as glioblastoma. Taken together, these findings likely reflect international disparities in both the quality of cancer registry practices as well as the accuracy and completeness of the pathological diagnoses of primary brain tumors. With such high levels of variance, and in some cases obscurity, in the histologies reported from country to country, it is difficult to imagine how current population-based cancer registries could accurately inform our understanding of the burden and prognosis of primary brain tumors on a global scale. Further, the potential paucity of molecularly informed diagnoses may exacerbate uninformed classification and outcome data. A key example of this pitfall is the breadth of subgroup classifications in pediatric tumors in recent years, ranging from embryonal tumors to gliomas.^6,7 Certainly, if there are large cohorts of “unspecified” tumors at the histologic level, this will only be magnified in the more contemporary classification systems, like the molecularly integrated World Health Organization (WHO) criteria.⁸ Such insufficiencies ultimately limit the collation of the smaller and smaller subgroups into clinically relevant global populations.

The results of this study should enable public health officials and agencies to prompt actions aimed at improving the reporting of brain and other tumors. Audits of cancer registry practices at both the local and national levels may be warranted, particularly among the methods used to collect data as these distinctions may at least partly contribute to discrepancies in incidence and survival outcome data.⁹ In addition, there needs to be close collaboration and data harmonization facilitated by the few organizations possessing the capability of coordinating cancer registries on an international scale, including the International Association of Cancer Registries, the Global Initiative for Cancer Registry Development, the International Cancer Control Partnership, the North American Association of Central Cancer Registries, the European Network of Cancer Registries, the African Cancer Registry Network, and others. By helping all countries train registry staff and strengthen local health information systems, coordinated international efforts to improve cancer registry practices would ultimately inform future studies of geographic differences in brain tumor survival, improve our understanding of the incidence of primary brain tumors by region and over time, and allow for more appropriate use of population-based data for public health decision making. This may require centralized funding and grant mechanisms to support these efforts as well. In countries where the necessary molecular testing is widely available, it is also critical that brain tumor registries keep pace with recent changes in the WHO Classification of Central Nervous Systems, as exemplified by the recent inclusion of molecular markers by the Central Brain Tumor Registry of the United States (CBTRUS).¹⁰ Incorporating these important changes in brain tumor taxonomy across the globe is necessary to ensure that brain tumor registry data will continue to be useful and consistent for researchers and health policy officials in the modern era. Further, in addressing inequities in data collection and ensuring cohesive reporting on a broad scale, we will be better equipped to bring impactful change to all children and adults with CNS tumors around the globe.