Mesothelioma incidence describes the number of new cases diagnosed in a population over some range of time. The study of mesothelioma cancer trends is a part of the larger science of mesothelioma epidemiology, which uses incidence rates to find patterns of the disease.
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Researching the incidence of asbestos-related cancers for specific groups of people is a major aspect of epidemiology. Whereas the prevalence of the disease only measures the total number of cases observed at any given time, the disease's incidence also reveals a group's overall risk for the disease.
Incidence rates are typically expressed as the number of potential cases per 100,000 people but can also be expressed in cases per million.
According to the National Cancer Institute’s Surveillance, Epidemiology and End Results (SEER) database, annual incidence rates for mesothelioma are holding steady around one new case per 100,000 people. Doctors diagnose approximately 3,000 new cases of mesothelioma each year in the U.S.
SEER tracks age-adjusted mesothelioma incidence rates from 1975 to 2014. Rates are down 9 percent from 2010 to 2014 — the latest available dataset — compared to the five years prior.
The incidence rate for Americans, in general, peaked in the late 1980s and early 1990s, topping out in 1992 at 1.49 cases per 100,000.
With data collected from epidemiological studies, researchers can identify the populations at highest risk for developing mesothelioma. By studying changes in the incidence rate and other trends over time, scientists can devise better measures for preventing asbestos diseases among these high-risk groups.
This also allows researchers to establish what factors may cause mesothelioma.
Because an overwhelming number of mesothelioma cases are caused by exposure to asbestos, U.S. and global trends of the disease are closely related to trends in asbestos exposure.
Mesothelioma has long been a male-dominated disease. Although men still represent an overwhelming majority of new cases, the gender gap is steadily closing with women now accounting for nearly one-fourth of all cases.
Incidence among men peaked in 1992, hitting 2.49 per 100,000. In comparison, the peak rate for women occurred in 1983 at 0.49 per 100,000. The ratio of incidence between men and women has been closer in the last 10 years than it has since SEER began tracking the data in 1975.
Overall, mesothelioma incidence in the U.S. has fluctuated minimally in the past few decades. The highest rates occurred from 1989 to 2002, with a rate of more than one case per 100,000 people each year in that span. In the last 10 years of data tracked by SEER, there has only been one year (2005) with an incidence above 1.
Multiple research studies have stated that the incidence of asbestos-related cancers in industrialized nations has not yet peaked but predict the number of cases will max out during the 2020s and 2030s. In the U.S., however, it is likely that the peak in mesothelioma incidence has already occurred.
The gender gap is closing as mesothelioma incidence rates among women are on the rise. Women now comprise nearly one-fourth of all cases.Read the Story
Mesothelioma carries an unusually long latency period of 20 to 50 years — the main reason why most patients are diagnosed at age 65 or older. According to the latest SEER report, people aged 80-84 have the highest mesothelioma incidence with 8.9 new cases per 100,000. Ages 85 and older are close behind with 8.5 new cases.
Women are nearly twice as likely to be diagnosed before age 65 compared to men. From 2009-2013, more women between ages 35-39 were diagnosed with mesothelioma than men in that age range.
After 65 years old, the gap in incidence between males and females continues to grow. The incidence for females is highest at ages 85 and older, but males in that category represent 19.1 cases per 100,000, the largest differential between genders for age-specific incidence.
Mesothelioma incidence is also influenced by race. At 0.5 new cases per 100,000, the rate for black Americans from 2005 to 2014 was much lower than the rate of 1 case per 100,000 for whites. However, blacks have the same incidence rate before age 65 than whites.
Although black men have a higher incidence compared to black women, the difference is significantly closer than that of white men and women.
Pleural mesothelioma — the most common of the four types — had an incidence rate of 3.05 cases per 100,000 people, according to a 2013 study from the Centers of Disease Control and Prevention (CDC).
The second-most-common type, peritoneal mesothelioma, had an age-adjusted incidence of only 0.21 cases. However, those under 45 years of age were just as likely to develop peritoneal mesothelioma as they were pleural.
The largest difference of incidence between types, 6.11 for pleural and 0.25 for peritoneal, occurred in patients 75 and older.
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Malignant mesothelioma is primarily attributed to asbestos exposure, and the majority of patients were first exposed to the toxic mineral while on the job.
Researchers have observed high rates of mesothelioma in regions and communities that relied heavily on asbestos, including places with a history of shipbuilding and industry.
According to the CDC report, mesothelioma incidence among the 50 U.S. states ranged from 0.58 to 1.65 per 100,000 people.
The average incidence rate among those states was 1.51.
From 1912 to 1980, Johns Manville Corporation operated a large asbestos manufacturing plant in Manville, New Jersey. Epidemiologists studied the impact of asbestos production on the borough's residents because many of them worked at the plant, where they were exposed to airborne fibers.
Mesothelioma rates in the Manville plant were roughly 25 times higher than the average statewide rates.
Geographical areas with naturally occurring deposits of asbestos have exhibited historically high rates of mesothelioma. Areas containing former asbestos mines are considered major mesothelioma hot spots.
Cities and regions in the U.S. with high mesothelioma incidence include:
Because the average life expectancy for mesothelioma patients is about a year, the disease's mortality and incidence are typically very close.
California is home to some of the largest deposits of naturally occurring asbestos in the world. The state leads the nation in mesothelioma deaths. In 2015 alone, California had 247 mesothelioma-related deaths, according to the CDC. In comparison, Florida, which is second to California, had 143 deaths.
The SEER age-adjusted incidence rate for California from 2010 to 2014 was 0.89 new cases per 100,000.
Fast Fact: One of the most prominent hot spots is Libby, Montana. This city was home to an asbestos-tainted vermiculite mine that was owned and operated by W.R. Grace and Co. for more than 40 years.
Researchers predict that New York City is also destined to become a hot spot. Because of the large clouds of asbestos dust released by the collapse of the Twin Towers at the World Trade Center, it is believed that mesothelioma could become a huge concern for New York City paramedics, police, firefighters or anyone else who lived in lower Manhattan immediately after the tragedy.
Although asbestos use is not officially banned in the U.S., government regulations severely restricted the toxic mineral's use since the 1970s. As a result, researchers believe the incidence of mesothelioma may have already peaked in the U.S.
Fast Fact: In the last 20 years tracked in the SEER database (1995-2014), the highest mesothelioma incidence was 1.16 in 1995.
Although mesothelioma cases in the U.S. appear to be on the decline, people exposed to asbestos decades ago will continue to develop the cancer in coming years because of its lengthy latency period.
One study projected approximately 85,000 cases from 2008 to 2054.
Today, most U.S. workers are exposed to asbestos through the demolition, renovation and maintenance of homes and buildings built before the 1980s.
Occupational asbestos exposure accounts for most of the world’s exposure to asbestos. In many of the world’s industrialized countries, workplace exposure to asbestos reached its peak and is receding. This is because the mining, consumption and manufacturing of asbestos were banned outright, limited by law and regulation, or they declined because of an increased understanding of asbestos-related health risks.
The importation, production and use of asbestos and asbestos-containing products are banned in all 28 countries of the European Union. Australia and the United Kingdom — two nations with historically high incidence rates of mesothelioma — have comprehensive asbestos bans in place.
Canada plans to ban the toxic mineral by 2018, leaving the U.S. as the only major industrialized nation without a complete asbestos ban. Developing counties such as China, Kazakhstan, Russia, Brazil, India, Pakistan, Mexico, Indonesia and Thailand continue to use, produce and export asbestos. In these countries, asbestos exposure is still on the rise.
Researchers predict that ongoing asbestos consumption in developing nations will contribute to additional disease in the future but exactly how much is hard to quantify.
Precise analyses are difficult because data models differ from country to country. This is because of historic differences in asbestos exposure and consumption. In some countries, accurate data on asbestos use and disease are not available.
In addition, the cancer’s long latency period makes it difficult to predict mortality curves with speculative data.
Still, most researchers estimate that it will take at least another 50 years before mesothelioma and other asbestos-related cancers disappear.
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