Asbestos Exposure & Mesothelioma Cancer in Montana

Asbestos Exposure & Mesothelioma Cancer in Montana

Asbestos Exposure in Montana began when its mining became industrially important back in the 20th century. Asbestos and vermiculite were mined in several areas of Montana. Vermiculite is another insulating mineral.

There were several asbestos and/or vermiculite mines in Montana, all of them located in the western half of the state. Vermiculite Mountain, outside of the community of Libby, was the site of Montana’s largest vermiculite mine.

It operated from the 1920s until 1990. At one time, Vermiculite Mountain was the source of over 80% of the world’s vermiculite. Unfortunately, much of the vermiculite was contaminated with asbestos obtained from this mine.

This ore was shipped across Montana on its way around the world. Cascade County was a railroad transportation hub and some of the ore was processed at a plant in Great Falls.

Many residents of Montana worked in industries which mined, processed, or transported the vermiculite and asbestos ores. There was a large amount of human exposure to these minerals. Constructing homes and workplaces with asbestos insulation and other asbestos products may have also led to exposure.

Many of the people with mesothelioma in Montana lived along rail routes that pass through the population centers in the state. Most people in Montana live in these centers, so it is not necessarily unusual that people affected with mesothelioma would live along these routes as well.

Asbestos exposure

What do we know about mesothelioma in Montana?

Death certificates and tumor registry reports are two sources of information that can be used to learn about mesothelioma in Montana. Death certificates have been collected by Montana’s Office of Vital Statistics since the 1880s.

More recent death certificates have information on age, sex, place of residence, and type of employment, in addition to the cause of death.

The Montana Central Tumor Registry was established in 1979. This registry holds information on people with diagnosed cancers including their age, sex, and place of residence. The combination of these two data sources allows a more complete understanding of mesothelioma than either would provide alone.

By combining information from both the Montana Central Tumor Registry and Montana Death Registry, 200 Montanans were found who had been diagnosed with or died of mesothelioma between 1979 and 2002. Individuals in both registries were counted only once.

These people lived throughout the state, in counties with asbestos and vermiculite mines and in counties without mines.

Neither the tumor registry nor death certificates record time or place of asbestos exposure, so it is unknown whether these people were exposed to asbestos before they developed the disease.

Why did Montanans develop mesothelioma?

Asbestos exposure is the leading factor in developing mesothelioma, and it is believed that many of the Montanans with mesothelioma were exposed to asbestos. The Montana Tumor and Death Registries do not collect detailed histories on exposure, employment, or housing.

However, the primary industry in which a person worked is recorded at the time of death or diagnosis. This refers to one of the many possible employment areas in which a person may have worked during a lifetime.

While these industries may not indicate the source of asbestos exposure in all cases, they may help uncover useful patterns relating to employment and exposure potential.

The primary industries reported among mesothelioma patients in Montana were similar to the industries reported for a study of people who died of mesothelioma due to asbestos exposure from nineteen states in 1999. The industry named most often for both groups was construction. Homemaking was also high on both lists.

Although the numbers are relatively small, Montanans with mesothelioma tended to work in government, agriculture, or with the railroads in larger proportions than in the multi-state sample. Mining was captured under “other industries” in the multi-state group but could be identified separately on Montana records.

Eight (4%) of the Montana mesothelioma patients had mining listed as their primary industry. The industry was unknown for a large proportion (12%) of the Montana patients.

Industry comparisons only provide clues to a possible source of asbestos exposure; in-depth residential and employment histories are needed to determine where and when asbestos exposure may have occurred.

Who is affected by asbestos exposure in Montana?

The number of people with mesothelioma identified in Montana was 15 from 1979 to 1982 and 55 from 1999 to 2002. The population of Montana increased by 14% in this period. A comparison of national data to the combined Montana sample is not possible because no national database has used these methods to combine tumor and death registry records.

However, it is possible to compare Montana Central Tumor Registry records with those from the Surveillance, Epidemiology and End Results (SEER) registry.

SEER is a group of selected tumor registries around the country supported by the National Cancer Institute. The age-adjusted rate for mesothelioma in the SEER registries has remained relatively constant over the past twenty years.

The SEER registries reported about one person with mesothelioma for every 100,000 people each year from 1979 to 2002. Among the 200 people with mesothelioma in Montana, 178 were reported to the Montana Central Tumor Registry.


Asbestos exposure in Montana
Stats Analysis

The age-adjusted rate of mesothelioma due to asbestos exposure in the Montana Central Tumor Registry tripled from 1979 to 2002. In 1979, 0.4 per 100,000 Montanans were diagnosed with mesothelioma.

By 2002, 1.2 per 100,000 people in Montana were diagnosed with mesothelioma. These rates come from small numbers of people with mesothelioma, and much of this variation may be due to chance.

Most people are not diagnosed until they are over 60 years old because mesothelioma develops very slowly. The median age at diagnosis for Montanans with mesothelioma cancer was 70 years for men and 71 years for women.

Since mesothelioma may take 20 to 40 years to develop, it is not often found in younger age groups. The vast majority (81%) of people with mesothelioma cancer in Montana were over 60 years of age when they were diagnosed.

More than three-quarters (78%) of the Montanans diagnosed with mesothelioma were men. The length of survival from time of diagnosis could be calculated for 172 Montanans with mesothelioma who died prior to 2002. The median length of survival was 5.5 months.

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