Environment and Breast Cancer: Science Review

Evidence From Humans
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Occupation and cancer - follow-up of 15 million people in five Nordic countries
Pukkala, E., Martinsen, J. I., Lynge, E., Gunnarsdottir, H. K., Sparen, P., Tryggvadottir, L., Weiderpass, E., Kjaerheim, K. Acta Oncol. 2009. 48:5, 646-790.
Topic area
Environmental pollutant - Occupation
Study design
Prospective record linkage
Funding agency
Nordic Cancer Union Scientific Council, Sweden
Study Participants
Number of Cases
373,361 cases of female breast cancer, 375,697 including male breast cancer
Menopausal Status
The menopausal status of women included in this study is listed here.
No analysis based on menopausal status
Number in Cohort
Cohort: approximately 14.9 million
Country where study was conducted
Denmark, Finland, Iceland, Norway, Sweden
Cohort participation rate
Not applicable. This study was records-based.
Participant selection: Inclusion and exclusion criteria
Criteria used to select participants in the study.
The study population consists of all persons aged 30-64 identified in any computerized population census in the Nordic countries: Finland (1970, 1980, 1990), Sweden (1960, 1970, 1980, 1990), Norway (1960, 1970, 1980), Denmark (1970), Iceland (1981). Included were those between the ages of 30 to 64 years at the time the census took place and living in the same country on January 1st the following year. Individuals were followed in by linkage to national cancer registries until 2003 (Denmark/Norway), 2004 (Iceland) or 2005 (Finland/Sweden).
Exposure Investigated
Exposures investigated
Occupation obtained from first available Census questionnaire, coded based on either (1) NYK (Norway, Finland, Sweden), a Nordic adaptation of the International Classification of Occupations (ISCO), (2) Icelandic adaptation of ISCO or (3) national codes s
How exposure was measured
Questionnaire, self-administered
Exposure assessment comment
Exposure misclassification is a concern because analyses don’t account for changes in occupation during the study period. Authors note that validity studies of occupational categories assigned by census were generally good, but with underestimation of individuals who were economically active, particularly in agriculture (for example, work of married women in family business – such as agriculture – was not counted as occupational in 1960 Norwegian census).
Breast cancer outcome investigated
Primary incident breast cancer
Confounders considered
Other breast cancer risk factors, such as family history, age at first birth, and hormone replacement therapy use, that were taken into account in the study.
Genetic characterization included
If the study analyzed relationships between environmental factors and inherited genetic variations, this field will be marked Yes. No, if not.
Strength of associations reported
Breast cancer incidence in given occupation (as of first available census entry) compared to national incidence:

Technical workers: SIR 1.24 (95% CI 1.19-1.29)
Laboratory assistants: SIR 1.21 (95% CI 1.14-1.28)
Physicians: SIR 1.35 (95% CI 1.25-1.45)
Dentists: SIR 1.42 (95% CI 1.31-1.55)
Nurses: SIR 1.18 (95% CI 1.15-1.20)
Assistant nurses: SIR 0.95 (95% CI 0.93-0.97)
Other health workers: 1.14 (95% CI 1.11-1.17)
Artistic workers: SIR 1.26 (95% CI 1.18-1.33)
Farmers: SIR 0.78 (95% CI 0.76-0.80)
Gardeners: SIR 0.76 (95% CI 0.74-0.78)
Forestry workers: SIR 0.75 (95% CI 0.60-0.93)
Transport workers: SIR 1.15 (95% CI 1.04-1.27)
Drivers: SIR 0.81 (95% CI 0.75-0.88)
Textile workers: SIR 0.99 (95% CI 0.97-1.01)
Mechanics: SIR 0.93 CI 0.88-0.97)
Painters: SIR 0.93 (95% CI 0.78-1.10)
Chemical process workers: SIR 0.90 (95% CI 0.84-0.97)
Beverage workers: SIR 1.04 (95% CI 0.92-1.19)
Welders: SIR 0.75 (95% CI 0.59-0.95)
Printers: SIR 1.15 (95% CI 1.09-1.22)
Engine operators: SIR 0.83 (95% CI 0.73-0.94)
Hairdressers: SIR 1.06 (95% CI 1.01-1.10)

Physicians: SIR 1.05 (95% CI 0.52-1.88)
Dentists (5 cases): SIR 1.20 (95% CI 0.39-2.80)
Nurses (1 case): SIR 2.29 (95% CI 0.06-12.75)
Assistant nurses (2 cases): SIR 0.73 (95% CI 0.09-2.63)
Other health workers (11 cases): SIR 1.40 (95% CI 0.70-2.50)
Farmers: SIR 0.83 (95% CI 0.72-0.94)
Forestry workers: SIR 0.65 (95% CI 0.44-0.93)
Miners and quarry workers: SIR 1.55 (95% CI 0.90-2.49)
Mechanics: SIR 1.00 (95% CI 0.86-1.17)
Painters: SIR 1.16 (95% CI 0.82-1.60)
Printers: SIR 1.86 (95% CI 1.28-2.59)
Building caretakers: SIR 1.59 (95% CI 1.13-2.17)
Results Comments
This study considered many additional job titles. We focus on (1) significant positive associations (2) if a particular job or sector was significantly associated with breast cancer in at least one study, we report results from all other studies that considered that sector, regardless of significance. It is important to note that job coding criteria generally differed across studies. Authors report that results were similar in an analysis of Finnish data restricted to those whose occupation was stable across follow-up censuses.
Author address
Finnish Cancer Registry, Institute for Statistical and Epidemiological Cancer Research, Pieni Roobertinkatu 9, FI-00130, Helsinki, Finland. eero.pukkala@cancer.fi