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ORAL 23 - Prevention and Cancer Risk (ID 121)
- Event: WCLC 2015
- Type: Oral Session
- Track: Prevention and Tobacco Control
- Presentations: 1
ORAL23.05 - Increased Proportion of Female and Young Mesothelioma Cases Are Indicators of Environmental Exposure to Carcinogenic Mineral Fibers in Nevada (ID 959)
10:45 - 12:15 | Author(s): R.V. Metcalf
Inhalation of asbestos and other carcinogenic mineral fibers cause malignant mesothelioma (MM) and lung cancer. Occupational exposure leads to a MM male to female (M:F) sex-ratio of 4-8:1, with a mean age of diagnosis of 74 years old because of the 30-50 years latency between initial exposure and MM development. In places where people are only environmentally exposed to carcinogenic fibers, the M:F sex-ratio is about 1:1 and the mean age of diagnosis is 50-60 years. In places where both types of exposure exist, the M:F sex ratio decreases and the proportion of young (<55 years old) cases increases, compared to places with occupational exposure only. Therefore, incidence rates cannot distinguish between occupationally- and environmentally-caused mesotheliomas.
In order to detect areas with possible environmental exposure to carcinogenic fibers, we studied the geology of Nevada. We compiled and integrated known presence of fibrous minerals in Nevada from published sources. We used the CDC 2006-2010 cancer data to study MM incidence and death rates by state and by gender. We also analyzed MM mortality data from the CDC in different Nevada Counties, per sex and age group, for the 1999-2010 period.
Several fibrous minerals were identified in Nevada, including actinolite asbestos, other amphiboles such as magnesioriebeckite, winchite and richterite that caused an epidemic of asbestos-related disease in Libby, Montana, and the highly carcinogenic erionite. For the 2006-2010 period, Nevada has a global MM age-standardized incidence rate of 10 cases per million inhabitants-year (95% confidence interval (CI): 8-12), similar to the average MM rate in the US (10 per million; 95% CI: 10-10). We discovered that Clark and Nye counties in southern Nevada had higher proportion of young (<55 years) MM cases (11.28%) and lower M:F sex-ratio (2.69:1), compared with other Nevada counties (M:F sex-ratio=6.33:1, p=0.04; proportion of young MMs=9.09%, p=0.80) and with the US (M:F sex-ratio=4.97:1, p=0.04; proportion of young MMs=6.21%, p=0.02).
The significant decrease of MM M:F sex-ratio and increase of young cases are indicators of possible environmental exposure to carcinogenic fibers in southern Nevada. In this arid region, naturally occurring asbestos minerals are present in urban and rural areas where people use to enjoy outdoor activities including horseback riding, running, hiking, bicycling, and off-road vehicle (ORV) recreation. Airborne dust is common due to wind erosion. Asbestos fibers have been found in air and dust samples in Clark County. Further research should be conducted in this area to help identify sources of environmental exposure to these mineral fibers, activities that lead to the release of these carcinogenic fibers into the air, and measures to reduce the consequent risk of MM and other cancers.
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