BE AWARE: Cases of Mesothelioma are Under Reported

Cases of malignant mesothelioma, caused almost exclusively by exposure to asbestos, are significantly underreported worldwide, concludes a new study published online January 6 in Environmental Health Perspectives. This study is the first to provide a global estimate of unreported cases. Many underdeveloped countries do not report mesothelioma, despite extensive use of asbestos. Because there is a […]

Cases of malignant mesothelioma, caused almost exclusively by exposure to asbestos, are significantly underreported worldwide, concludes a new study published online January 6 in Environmental Health Perspectives.

This study is the first to provide a global estimate of unreported cases. Many underdeveloped countries do not report mesothelioma, despite extensive use of asbestos. Because there is a direct link between the 2, the study authors used data from countries that do report mesothelioma to extrapolate to the countries that do not. Their conclusion: for every 4 to 5 reported cases of mesothelioma worldwide, at least 1 case goes unreported.

“Our most important finding is the magnitude of unreported mesothelioma in countries that use asbestos at substantial levels but report no cases of the disease,” study coauthor Ken Takahashi, MD, from the University of Occupation and Environmental Health, Kitakyushu City, Japan, said in a statement. Such countries include Russia, Kazakhstan, China, and India, which all rank in the top 15 countries for cumulative asbestos use.

The authors propose a worldwide ban on the mining, use, and export of asbestos, because eliminating exposure to asbestos would prevent mesothelioma.

A number of countries have already adopted bans on asbestos use on the grounds of public heath, they note. However, the use of asbestos worldwide is increasing, they add.

Extrapolating to Find “Missing” Cases

The authors identified 56 countries that had data on both mesothelioma frequency and asbestos use, and another 33 that had data on asbestos use but no data on mesothelioma cases.

Together, these data account for 100% of global asbestos use from 1920 to 1970.

By individual country, cumulative asbestos use was highly skewed, led by the United States, Russia, the United Kingdom, Germany, and Japan.

The authors calculated 15-year cumulative mortality from mesothelioma from 1994 to 2008. This was also highly skewed, and generally paralleled the level of cumulative asbestos use, with the leading countries being the United States, United Kingdom, Italy, Germany, and France.

There was a clear and statistically significant positive linear relation between the cumulative use of asbestos from 1920 to 1970 and the cumulative number mesothelioma deaths from 1984 to 2008 in the countries with recorded cases.

The researchers used this relation to estimate the number of cases that would be expected in the countries that did not report mesothelioma cases but did report asbestos use.

For the 56 countries that reported both mesothelioma occurrence and asbestos use, the 15-year cumulative number of mesothelioma cases was approximately 174,300.

Extrapolating this number to the 33 countries that did not report cases, the researchers calculated that they had a total of 38,900 cases.

In this group, the leading countries for the predicted 15-year mesothelioma mortality were Russia, Kazakhstan, China, India, and Thailand.

“The present study is the first to provide a global estimate of ‘missed’ mesothelioma cases, accounting for the collective experience of countries with data,” the authors conclude.

One of the limitations of this study is that the extrapolation went from a group of 56 countries that included both developed and developing countries, to a group of 33 countries that were predominantly developing; this might have introduced bias, the researchers note. In addition, there is no information about how the data on consumed asbestos relate to the actual exposure levels, or on the fiber types involved (e.g., amphiboles, chrysotile). The researchers also point out that smoking is not related to mesothelioma, so confounding need not be accounted for.

Likely to Be an Underestimate

Despite pointing out these cautions, the researchers believe that their findings underestimate the size of the problem, because the data that are available are likely to represent underreporting of cases of mesothelioma and asbestos use.

“Our values should be viewed as conservative estimates,” they note.

“It is plausible that the ‘hidden’ burden is substantial in countries with high cumulative use of asbestos, including the asbestos-producing countries, such as Russia, Kazakhstan, China, and India,” the authors explain. For countries with a vested interest in maintaining production and trade in asbestos, there might be a policy of not actively disclosing cases of mesothelioma to the international community, because an increasing number of countries are adopting bans on asbestos on public health grounds, they note.

In addition, there has been a sharp increase in the use of asbestos worldwide. The cumulative use of asbestos up to 1970 (65 million metric tons) has doubled since then (to 124 million metric tons), the researchers report.

In particular, the group of 33 countries that do not disclose mesothelioma cases have increased their use of asbestos 5-fold, they point out.

Before 1970, cumulative use exceeded 3 million metric tons in 5 countries: the United States (21.8 million metric tons), Russia (8.4), the United Kingdom (4.8), Germany (4.1), and Japan (3.1).

After 1971, there were 8 countries exceeding this amount: Russia (36.1 million metric tons), China (11.2), Kazakhstan (9.6), Japan (8.1), the United States (6.9), Brazil (5.3), Germany (5.2), India (4.5), and Thailand (3.6).

“Thus, even with the expected hygienic improvements to reduce exposure over time, particularly since 1970 onward, these countries should anticipate the need to deal with a very high burden of mesothelioma in the immediate decades ahead,” the authors warn.

This study was supported in part by the Japan Society for the Promotion of Sciences Asia Africa Science Platform. The researchers have disclosed no relevant financial relationships.

Environ Health Perspect. Published online January 6, 2011.

 

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