A case-control study of lung cancer mortality in six Gila Basin, Arizona smelter towns

Our plain-English summary of A case-control study of lung cancer mortality in six Gila Basin, Arizona smelter towns, by G.M. Marsh, R.A. Stone, N.A. Esmen, et al (Environmental Research, 1997).

The study

• Authors: G.M. Marsh, R.A. Stone, N.A. Esmen, M.J. Gula, C.K. Gause, N.J. Petersen, F.J. Meaney, S. Rodney, D. Prybylski
• Journal: Environmental Research
• Published: 1997;75(1):56-72
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

To investigate factors related to lung cancer mortality in six Arizona copper smelter towns, we identified 185 lung cancer cases and two matched controls per case from decedent residents during 1979-1990. Detailed information on lifetime residential, occupational, and smoking history was obtained by structured telephone interviews with knowledgeable informants. Interviews were completed for 82% of 183 eligible cases and 88% of the targeted number (366) of controls. Estimated historical environmental exposures to smelter emissions, based on atmospheric diffusion modeling of measured SO2 concentrations, were linked with residential histories to derive individual profiles of residential exposure. Occupational histories were characterized by potential exposure to smelter emissions, asbestos, and ionizing radiation. Conditional logistic regression was used to compare study factors in cases and controls with adjustment for potential confounding factors: gender, Hispanic ethnicity, and smoking. In overall and gender-specific analyses, no statistically significant associations were observed between lung cancer risk and any of the measures of residential exposure to smelter emissions considered (town of residence at time of death, highest level of exposure, and duration or cumulative exposure above background levels), or any of the estimated occupational exposures (definite or potential asbestos, potential ionizing radiation, definite or potential smelter). Among male residents of some, but not all, towns, there was some evidence of a positive association between lung cancer risk and reported copper smelter-related employment (reported as definite), with the highest risk observed for Miami, Arizona. This study provided little evidence of a positive association between lung cancer mortality and residential exposure to smelter emissions. Specific factors associated with the apparent heterogeneity in lung cancer risk across study towns cannot be identified in this community-based study.

In plain English

This population-based matched case-control study examined lung cancer deaths in six Arizona copper smelter towns. Cases died of lung cancer in 1979–1990; controls died of other causes, excluding respiratory cancer, skin cancer and arsenic poisoning. Telephone interviews with informants covered 150 cases and 322 controls. Home smelter exposure was estimated by modelling sulfur dioxide measurements. Jobs were rated for possible smelter, asbestos and ionizing radiation exposure. In models adjusted for gender, Hispanic ethnicity and smoking, smokers had an estimated 6.80 times the odds of lung cancer death of nonsmokers (95% confidence interval 3.30 to 13.99). In the overall and gender-specific analyses, no statistically significant association was found for residential smelter exposure or any job exposure. Definite occupational asbestos exposure had an odds ratio of 0.97 (95% confidence interval 0.31 to 2.96); only 12 men had it. Miami men reporting smelter work had an odds ratio of 4.00 (1.14 to 14.06) versus Miami men without it. The authors concluded there was little evidence linking residential smelter emissions to lung cancer. They noted apparent recall bias in reported asbestos jobs; home asbestos exposure could not be assessed.

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: Population-based matched case-control study of deaths. Cases and controls were decedents, and information came from proxy informants by structured telephone interview.
• Who was studied: Residents of six Gila Basin, Arizona copper smelter towns (Globe, Hayden, Kearny, Miami, Superior, Winkelman) who died between 1979 and 1990. Of 185 lung cancer cases first identified, 2 were excluded, leaving 183. Interviews were completed for 150 cases (82.0%) and for 322 controls (88.0% of the target of 366). Controls were decedent residents from the same period, matched on age and time of death. Deaths from respiratory cancer, skin cancer, and acute or chronic arsenic poisoning were excluded from the control pool.
• Exposure: Residential exposure to smelter emissions was estimated from atmospheric diffusion modelling of measured sulfur dioxide (SO2) and linked to each person's residential history. Occupational exposure to smelter emissions, asbestos and ionizing radiation was assigned from reported job titles. No asbestos fiber type is named. Smoking was also assessed.
• Main results:
  • All cases and controls: smokers had an estimated 6.8 times the odds of lung cancer compared with otherwise similar nonsmokers (odds ratio 6.80, 95% CI 3.30 to 13.99). This estimate comes from the base model, which included gender, Hispanic ethnicity and smoking.
  • All cases and controls, adjusted for gender, Hispanic ethnicity and smoking: there was little evidence of an association between lung cancer and any measure of residential exposure to smelter emissions (P greater than 0.44 for each).
  • All cases and controls: no statistically significant associations were found with any estimated occupational exposure (P greater than 0.63 for each). Odds ratios ranged from 0.9 to 1.13.
  • Gender-specific analyses: no statistically significant associations were found for any estimated occupational exposure for males (P greater than 0.32) or females (P greater than 0.50).
  • All cases and controls: definite occupational asbestos exposure had an odds ratio of 0.97 (95% CI 0.31 to 2.96), global test P value 0.95. Potential asbestos exposure had an odds ratio of 0.93 (95% CI 0.54 to 1.61).
  • Males only: definite occupational asbestos exposure had an odds ratio of 1.08 (95% CI 0.30 to 3.82), P value 0.91.
  • Only 12 male decedents had definite occupational asbestos exposure. Most male cases and controls in each town had no potential occupational asbestos exposure.
  • Within-town analysis: male decedents in Kearny, Superior and Miami with definite occupational smelter exposure had odds ratios of 3.11, 4.95 and 4.00 respectively. These were compared with men in the same town who never worked in a copper smelter. The confidence intervals were wide, and only the Miami estimate was statistically significantly elevated.
  • Miami males with definite occupational smelter exposure, compared with Miami males without it, had an odds ratio of 4.00 (95% CI 1.14 to 14.06).
• The authors' conclusion: The authors concluded that the study provided little evidence of a positive association between lung cancer risk and residential exposure to smelter emissions. They found some evidence that the association with reported smelter employment differed by town, with Miami men at highest estimated risk.
• Limitations the authors state:
  • The authors found evidence of recall bias in reported asbestos exposure, because many informant-reported asbestos-related occupations were improbable.
  • Residential asbestos exposure could not be assessed, so the study is not informative about its health effects.
  • Occupational exposures were assigned from job titles with substantial uncertainty, and it could not be determined whether workers were actually exposed.
  • Historical residential exposures were not directly measured. Very few air data existed before 1970, so most exposure estimates were extrapolated back in time.
  • Estimated residential exposure varied little among residents, which limited the study's power to detect health effects.
  • Lung cancer mortality rates and expected deaths could not be computed, because the population at risk could not be enumerated.
  • Town of residence at death may not have been the place where the person was employed.

Topics

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

Medical terms in this study, explained in our Lexicon: Case-Control Study, Lung Cancer, Environmental Exposure, Confounding, Cumulative Exposure, Occupational Exposure.

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