Residential proximity to naturally occurring asbestos and mesothelioma risk in California

Our plain-English summary of Residential proximity to naturally occurring asbestos and mesothelioma risk in California, by X.L. Pan, H.W. Day, W. Wang, et al (American Journal of Respiratory and Critical Care Medicine, 2005).

The study

• Authors: X.L. Pan, H.W. Day, W. Wang, L.A. Beckett, M.B. Schenker
• Journal: American Journal of Respiratory and Critical Care Medicine
• Published: 2005;172(8):1019-25
• Cited by: 98 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Rationale: Little is known about environmental exposure to low levels of naturally occurring asbestos (NOA) and malignant mesothelioma (MM) risk.

Objectives: To conduct a cancer registry-based case control study of residential proximity to NOA with MM in California.

Methods: Incident MM cases (n = 2,908) aged 35 yr or more, diagnosed between 1988 and 1997, were selected from the California Cancer Registry and frequency matched to control subjects with pancreatic cancer (n = 2,908) by 5-yr age group and sex. Control subjects were selected by stratified random sampling from 28,123 incident pancreatic cancers in the same time period. We located 93.7% of subjects at the house or street level at initial diagnosis. Individual occupational exposure to asbestos was derived from the longest held occupation, available for 74% of MM cases and 63% of pancreatic cancers. Occupational exposure to asbestos was determined by a priori classification and confirmed by association with mesothelioma.

Main Results: The adjusted odds ratios and 95% confidence interval for low, medium, and high probabilities of occupational exposures to asbestos were 1.71 (1.32-2.21), 2.51 (1.91-3.30), and 14.94 (8.37-26.67), respectively. Logistic regression analysis from a subset of 1,133 mesothelioma cases and 890 control subjects with pancreatic cancer showed that the odds of mesothelioma decreased approximately 6.3% for every 10 km farther from the nearest asbestos source, an odds ratio of 0.937 (95% confidence interval = 0.895-0.982), adjusted for age, sex, and occupational exposure to asbestos.

Conclusions: These data support the hypothesis that residential proximity to NOA is significantly associated with increased risk of MM in California.

In plain English

This case-control study used the California Cancer Registry. The authors compared 2,908 people aged 35 or older diagnosed with malignant mesothelioma in 1988 to 1997 with 2,908 age- and sex-matched pancreatic cancer patients. No map of naturally occurring asbestos in California existed, so distance was measured from each address at diagnosis to the nearest known ultramafic rock, used as a stand-in for natural asbestos. Two small Southern California deposits were excluded. Occupational asbestos exposure was estimated from registry occupation records. In the main analysis of 1,133 cases and 890 controls within 100 km of such rock, adjusted for age, sex and occupation, the odds of mesothelioma were about 6.3% lower for every 10 km farther away (odds ratio 0.937, 95% CI 0.895 to 0.982). This was statistically significant in men but not in women. People whose occupation had a high probability of asbestos exposure had an adjusted odds ratio of 14.94 (95% CI 8.37 to 26.67) compared with no recognizable exposure. The authors concluded the data support an association between living near naturally occurring asbestos and mesothelioma. They noted that work and residence histories were incomplete.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Cancer registry-based case-control study, with pancreatic cancer patients as controls
• Who was studied: 2,908 malignant mesothelioma cases (2,354 men, 554 women) aged 35 or older, diagnosed 1988 to 1997 and reported to the California Cancer Registry. Controls were 2,908 pancreatic cancer patients, frequency matched by 5-year age group and sex and sampled from 28,123 pancreatic cancers in the same period. Regression analyses used a subset of 1,133 cases and 890 controls with complete data.
• Exposure: Distance from the residential address at diagnosis to the edge of the nearest known body of ultramafic rock, used as a proxy for naturally occurring asbestos because no map of naturally occurring asbestos in California existed. Two small Southern California deposits were excluded from the distance calculation. Occupational asbestos exposure was ranked as none, low, moderate or high probability from the longest-held occupation or industry.
• Main results:
  • Among all subjects in the regression subset (1,133 cases, 890 controls), the odds of mesothelioma were 6.3% lower for every 10 km farther from the nearest asbestos source: odds ratio 0.937 (95% CI 0.895 to 0.982), p 0.006. This was adjusted for age, sex and occupational exposure.
  • By sex, the odds ratio per 10 km was 0.935 (95% CI 0.888 to 0.985, p 0.011) for men (962 cases, 746 controls). For women (171 cases, 144 controls) it was 0.952 (95% CI 0.853 to 1.062, p 0.381), which was not statistically significant.
  • Compared with no recognizable occupational exposure (the reference group), the adjusted odds ratios for mesothelioma were 1.71 (1.32 to 2.21) for low, 2.51 (1.91 to 3.30) for medium and 14.94 (8.37 to 26.67) for high probability of occupational asbestos exposure.
  • In an analysis excluding cases with moderate or high probability of occupational exposure, results were very similar. The odds ratio per 10 km was 0.939 (95% CI 0.887 to 0.994) for men and 0.961 (95% CI 0.861 to 1.073) for women.
  • Pleural mesotheliomas were 91% of cases. Among pleural cases only, proximity was significantly associated with case status in both men and women. Among peritoneal cases only, proximity was not significantly associated and showed no trend with distance.
  • Median distance to the nearest ultramafic rock was 55.2 km for male cases versus 115.5 km for male controls, and 112.3 km for female cases versus 131.4 km for female controls.
• The authors' conclusion: The authors concluded that the data support the hypothesis that living near naturally occurring asbestos is significantly associated with increased mesothelioma risk in California. They described this as an independent and dose-response association.
• Limitations the authors state:
  • Lifetime occupational histories were incomplete; the registry often listed only the current or most recent occupation.
  • There was no reliable job-exposure matrix, so misclassification of occupational exposure was unavoidable.
  • Only the address at diagnosis was available; lifetime residential history was lacking.
  • The map showed ultramafic rock, not asbestos itself.
  • The study could not control for domestic or residential asbestos exposure from other sources.
  • Mesothelioma patients may have been asked more about their occupation, which may have led to overestimating occupational exposure.
  • Results in women were based on small samples and were not statistically significant.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Mesothelioma.

Medical terms in this study, explained in our Lexicon: naturally occurring asbestos (NOA), Mesothelioma, Environmental Exposure, Malignant Mesothelioma, Cancer Registry, Occupational Exposure, Odds Ratio, confidence interval.

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• Increased risk of malignant mesothelioma of the pleura after residential or domestic exposure to asbestos: a case-control study in Casale Monferrato, Italy — C. Magnani, P. Dalmasso, et al. (2001)
• Age and sex differences in malignant mesothelioma after residential exposure to blue asbestos (crocidolite) — A. Reid, G. Berry, et al. (2007)

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