Mesothelioma Rates Declining Four Decades After Most Use of Asbestos Banned in U.S.: Study

It has taken this long for mesothelioma rates to decline due to the long latency period of the disease, which can appear decades after asbestos exposure.

Mesothelioma rates linked to asbestos exposure have finally begun to decrease, decades after most uses of the cancer-causing substance were banned in the United States, according to the findings of a new study.

One of the few known causes of mesothelioma cancer is exposure to asbestos fibers, which were used in a variety of manufacturing and building industries until most uses were banned in 1972. The condition is nearly always fatal, as it is often not diagnosed until the cancer is already at a very advanced stage, resulting in a very short life-expectancy after diagnosis.

Researchers with Duke University say those bans are finally resulting in decreasing mesothelioma diagnoses. They say it has taken this long for the rates to drop because mesothelioma has a long latency period, meaning it can take decades before symptoms become obvious and a diagnosis is made. Their findings were published in the August issue of Environmental Research.

Mesothelioma lawsuits are part of the largest mass-tort in U.S. history, with more than 600,000 people having filed a case against more than 6,000 defendants due to injuries caused by inhaling asbestos fibers. In addition to individuals directly exposed to asbestos, a growing number of the lawsuits filed in recent years have involved second-hand exposure among individuals who inhaled fibers carried on on the clothes or in the hair of their parents when they were children.

The researchers performed a fiber analysis involving more than 600 mesothelioma cases reported over the past 40 years, looking for fiber types, concentrations, and incidents of mesothelioma not linked to asbestos exposure. While rare, mesothelioma can occur in idiopathic and spontaneous cases, although some say many of these cases may be caused by unknown past asbestos exposures.

According to their findings, mesothelioma diagnoses have shifted to older patients, an increasing percentage of women, and an increase in peritoneal cases. The researchers report that the percentage of patients with concomitant asbestosis has also decreased over tome.

Cases of mesothelioma involving elevated lung asbestos content decreased from 90.5% in the 1980s, to 54.1% by the 2010s, the data indicates. In the 1980s, 91.8% of mesothelioma diagnoses were in men, but that percentage decreased to 65.1% by the 2010s.

“In conclusion, we have shown that asbestos fiber content of lung tissue has steadily decreased over the past four decades, with a concomitant increase in the relative proportion of cases that are not asbestos related. These findings are associated with an increase in the median age of mesothelioma patients and an increased percentage of epithelial histological pattern,” the researchers determined. “The percentage of cases with concomitant asbestosis has markedly decreased and approached nil.”

Mesothelioma and Asbestos Still a Health Threat

In 2017, the U.S. Centers for Disease Control and Prevention reported that, from 1999 to 2015, the annual mesothelioma death rate had increased by 4.8% from 2,479 deaths in 1999 to 2,579 deaths in 2015. That was higher than expected at the time, since the CDC had previously projected the rates to start decreasing after 2005.

Last month, the U.S. Environmental Protection Agency (EPA) announced the final approval of a new asbestos reporting rule, which will require companies that still manufacture or process asbestos or asbestos-containing materials to disclose the quantities of asbestos, types used, and provide data on employee asbestos exposure events.

The EPA indicates this will be a one-time reporting requirement, covering the prior four years. Manufacturers, importers and processors will have nine months after the rule is effective to submit the required data.

The information will be used by the EPA and other federal agencies in considering potential future regulatory actions. This may include risk evaluation and risk management activities.

The asbestos reporting rule was proposed following a final risk evaluation issued by the EPA in December 2020, which found unreasonable risks to human health from conditions of use associated with six categories of products that included asbestos use in the chlor-alkali industry, sheet gaskets and other types of gaskets and automotive brakes.

The final rule applies to any company who manufactured, imported or processed asbestos between 2019 and 2022 with annual sales above $500,000 during those years. The required information will include quantities of asbestos manufactured or processed, the type of asbestos used and employee data.