Breast cancer and occupational exposures in women in Finland

Our plain-English summary of Breast cancer and occupational exposures in women in Finland, by E. Weiderpass, E. Pukkala, T. Kauppinen, et al (American Journal of Industrial Medicine, 1999).

The study

• Authors: E. Weiderpass, E. Pukkala, T. Kauppinen, P. Mutanen, H. Paakkulainen, K. Vasama-Neuvonen, P. Boffetta, T. Partanen
• Journal: American Journal of Industrial Medicine
• Published: 1999;36(1):48-53
• Cited by: 57 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: The etiology of breast cancer is not fully understood. Environmental and occupational exposures may contribute to breast cancer risk.

Methods: We linked 324 job titles from the 1970 census of 892,591 Finnish women with incidence of breast cancer (23,638 cases) during 1971-1995. We converted job titles to 31 chemical and two ergonomic agents through a measurement-based, period-specific, national job-exposure matrix. Poisson regression models were fit to the data, with adjustment for birth cohort, follow-up period, socioeconomic status, mean number of children, mean age at first delivery, and turnover rate.

Results: For premenopausal breast cancer, medium/high level of occupational exposure to ionizing radiation was associated with a standardized incidence ratio (SIR) of 1.3 (95% confidence interval (CI) 0.7-2.5; trend P = 0.03). For postmenopausal breast cancer, we found on SIR of 1.2 (1.1-1.3) for low level and 1.4 (1.1-1.8) for medium/high level of ionizing radiation (trend P = 0.001); and an SIR 1.3 (1.1-1.7) for medium/high levels of both asbestos and man-made vitreous fibers. Aromatic hydrocarbon solvents showed a significant trend for a modest excess of postmenopausal breast cancer.

Conclusions: Our study indicates that occupational exposure to ionizing radiation may be associated with an increased risk of female breast cancer. High-quality studies on environmental and occupational etiology of breast cancer are needed for further elucidation of risk factors.

In plain English

This Finnish study linked the job titles of 892,591 women who reported an occupation in the 1970 census to breast cancers recorded by the Finnish Cancer Registry from 1971 to 1995. In that period, 23,638 breast cancers were diagnosed. Exposures, including asbestos, were estimated for each job title with a national job-exposure matrix. The analyses compared job groups, not individual women. For postmenopausal breast cancer (diagnosed at 50 or older), jobs with medium/high estimated asbestos exposure had a standardized incidence ratio of 1.32 (95% CI 1.05 to 1.67). The trend across exposure levels was not statistically significant (p = 0.16). This excess came from one case in miners and shot firers, four in insulators, and a slight excess in construction laborers. A similar excess for man-made vitreous fibers came from the same jobs, and the two exposures were strongly correlated in the data. Premenopausal cancer showed no significant asbestos excess. The authors concluded that occupational exposure to ionizing radiation may be associated with an increased risk of female breast cancer. They wrote that their asbestos and man-made vitreous fiber findings suggested an excess.

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: Census-based cohort followed through the cancer registry, analyzed at aggregated (ecological) job-title level using a job-exposure matrix and Poisson regression
• Who was studied: 892,591 Finnish women who reported an occupation in the 1970 census, followed for cancer from 1971 through 1995 (15,481,680 person-years, 23,638 primary breast cancers). Premenopausal cancer was defined as diagnosis before age 50 and postmenopausal as age 50 or more.
• Exposure: Thirty-one chemical agents (including asbestos and man-made vitreous fibers; asbestos fiber type not specified) and two ergonomic agents, estimated per job title from the Finnish national job-exposure matrix (FINJEM). Exposure was graded as zero, low or medium/high.
• Main results:
  • Postmenopausal breast cancer, asbestos: medium/high exposure level SIR 1.3 (Table II: 1.32, 95% CI 1.05 to 1.67). Low level SIR 0.98 (0.85 to 1.12). Trend p = 0.16.
  • The postmenopausal asbestos excess at medium/high level came partly from one case among miners and shot firers (rock blasting workers): SIR 2.7, 95% CI 0.04 to 15.0.
  • The rest of the asbestos excess came from four cases among insulators (SIR 2.3; 95% CI 0.6 to 5.8) and a slight excess in construction laborers (SIR 1.1; 95% CI 0.8 to 1.4; 68 cases).
  • Man-made vitreous fibers showed a similar postmenopausal excess (medium/high SIR 1.32, 95% CI 1.05 to 1.66; trend p = 0.10), derived from the same jobs. Asbestos and man-made vitreous fibers were strongly correlated in the data.
  • With exposure divided into four levels, the postmenopausal asbestos trend was flat until the highest category (SIR 1.3; trend p = 0.11).
  • Premenopausal breast cancer, asbestos (Table I): low level SIR 1.04 (95% CI 0.81 to 1.33), medium/high level SIR 1.12 (95% CI 0.71 to 1.76), trend p = 0.58.
  • The authors wrote that their findings for asbestos and/or man-made vitreous fibers suggested an excess.
  • Postmenopausal breast cancer, ionizing radiation: low level SIR 1.2 (Table II: 1.22, 95% CI 1.12 to 1.33), medium/high SIR 1.4 (1.41, 95% CI 1.12 to 1.77), trend p less than 0.001.
  • Premenopausal breast cancer, ionizing radiation showed a significant trend (p = 0.03). In Table I, low level SIR 1.30 (95% CI 1.02 to 1.67) and medium/high level SIR 1.34 (95% CI 0.72 to 2.52).
  • Aromatic hydrocarbon solvents showed a significant trend for postmenopausal breast cancer (SIR 1.2 at the highest of four levels).
• The authors' conclusion: The authors concluded that occupational exposure to ionizing radiation may be associated with an increased risk of female breast cancer. They called for further high-quality studies.
• Limitations the authors state:
  • The data were aggregated by job (ecological), so variation within jobs in cancer rates, exposures and covariates was incompletely accounted for.
  • The job-exposure matrix does not distinguish women from men, and some job categories have mixed exposures.
  • Job titles came from a single point in time (the 1970 census).
  • Menopausal status was defined only by age, and number of children and age at first birth were available only as averages for each occupational group.
  • Both excesses and deficits may be biased toward no effect because of aggregate-level data and misclassification.
  • The ionizing radiation excesses were driven largely by physicians and nurses. The authors questioned whether radiation played a role in these groups, since only an estimated 0.3% of them are exposed to X-rays.

Topics

Medical terms in this study, explained in our Lexicon: Occupational Exposure, Etiology, Standardized Incidence Ratio (SIR), confidence interval, Vitreous.

Related studies

• Women's occupation and cancer: preliminary analysis of cancer registrations in England and Wales, 1971-1990 — J. Simpson, E. Roman, et al. (1999)
• Occupational risk factors for lung cancer in women: results of a case-control study in Germany — I. Jahn, W. Ahrens, et al. (1999)
• Gynecologic and breast cancers in women after exposure to blue asbestos at Wittenoom — A. Reid, A. Segal, et al. (2009)
• Occupational exposures and male breast cancer: A nested case-control study in the Nordic countries — M. Talibov, J. Hansen, et al. (2019)
• A Cohort Study on Cancer Incidence among Women Exposed to Environmental Asbestos in Childhood with a Focus on Female Cancers, including Breast Cancer — S.B. Dalsgaard, E.T. Würtz, et al. (2022)
• Occupational exposures and risk of stomach cancer by histological type — M. Santibañez, J. Alguacil, et al. (2012)

Browse more research in American Journal of Industrial Medicine, or return to medical research.