The international histology distribution of brain tumors varies greatly, suggesting disparities in registration practices and data quality, according to a study in Neuro-Oncology.
Investigators analyzed data from 286 of the 322 population-based cancer registries participating in the CONCORD-3 study, which included 67,331 children and 671,085 adults diagnosed with a primary brain tumor in 60 countries from 2000 to 2014. The analysis included 59 countries, excluding Mexico because the records did not have a valid morphology code.
A total of 12 histology groups were defined for children and 11 for adults. The final study population included 60,783 (90.3%) children (aged 0-14 years) and 602,112 (89.7%) adults (aged 15-99 years) after exclusion of irrelevant morphology codes.
The researchers reported trends for patients diagnosed from 2000 to 2004, 2005 to 2009, and 2010 to 2014 by country and histology group but focused their comments on the histology distribution for 2005 to 2009, when proportions were more robust than for 2000 to 2004 and 2010 to 2014.
Among children diagnosed from 2005 to 2009, the proportion of brain tumors classified as low-grade astrocytoma (World Health Organization [WHO] grade 1 or 2) ranged from less than 10% in some African countries, for example, to more than 30% in the United States and the United Kingdom, among other countries. High-grade astrocytomas (WHO grade 3 or 4) accounted for less than 10% of all brain tumors in countries such as Canada and the United States, and ranged from 10% to 20% elsewhere. Unspecified astrocytomas accounted for less than 10% of brain tumors in 30 countries, with the highest levels occurring in the Russian Federation (27%).
Medulloblastomas accounted for less than 10% of brain tumors in some African countries, China, and others, with the highest rate of 31% occurring in Jordan and Taiwan.
In adults from 2005 to 2009, diffuse and anaplastic astrocytomas accounted for less than 10% of brain tumors in 26 countries. The proportion ranged from 10% to 19% in countries such as Argentina, Brazil, and the United States. The proportion of brain tumors classified as glioblastoma ranged from less than 10% in China to as high as 50% to 70% in North America and 21 of 28 European countries
Unspecified astrocytomas accounted for less than 10% of brain tumors in 43 countries among adults in this period, with the highest level in Ecuador (34%). Brain tumors of unspecified histology accounted for less than 10% of brain tumors in 28 countries, with the highest levels in Algeria and China (65%).
In overall analysis from 2000 to 2014 among children, low-grade astrocytomas were histologically verified in 100% of cases in 38 countries. The range was 90% to 94% in countries including Canada and Australia, and 95% to 99% in the United States, Japan, and others.
From 2000 to 2014, the proportion of low-grade astrocytomas in children was relatively stable worldwide. In North America, the proportion of unspecified neoplasms in children increased from 2% to 6%. In adults, the proportion of glioblastomas in this period increased only in Europe (from 46% to 56%) and Oceania (from 57% to 65%). In North America, the proportion of unspecified neoplasms in adults increased from 6% to 12%
“There were striking international differences in the proportion of low-grade astrocytomas in children (ranging from 6% to 50% in 2005-2009),” stated the study authors.
The proportion of childhood medulloblastomas also varied widely between countries, offsetting the low proportion of low-grade astrocytomas in several countries, noted the authors. Among adults, the largest international variation was for glioblastomas (range, 9% to 69%). Wide international disparities were observed regarding some of the quality indicators, including the proportion of tumors with an unspecified histology, which was as high as 52% in children and 65% in adults, and the proportion of histologically verified tumors.
“The global variation in the histology distribution was remarkable,” the study authors commented. “We provided evidence that such variation may be mainly due to international differences in cancer registration practices, but also to wide disparities in the quality of data,” they concluded.
Girardi F, Rous B, Stiller CA, et al. The histology of brain tumours for 67,331 children and 671,085 adults diagnosed in 60 countries during 2000-2014: a global, population-based study (CONCORD-3). Neuro Oncol. Published online March 19, 2021. doi:10.1093/neuonc/noab067