Objectives The purpose of this study was to assess cancer incidence and cardiovascular mortality among women with a high dietary intake of fatty fish from the Baltic Sea (on the Swedish east coast), contaminated with persistent organochlorine compounds.

Material and methods Cohorts of fishermen's wives from the Swedish east (1989 subjects) and west (6605 subjects) coasts were established. The mortality and cancer incidence were studied in these cohorts, and comparisons were made with respective regional populations and between the cohorts. Dietary interviews were made with 200 randomly selected cohort women and equally many women from the general population. The interviewed east- and westcoast cohort women ate locally caught fatty fish at least twice as often as their referents.

Results Compared with that of the regional population, the breast cancer incidence was higher than expected in the eastcoast cohort [standardized incidence ratio (SIR) 1.29, 95% confidence interval (95% CI) 0.96--1.71], whereas it was lower in the westcoast cohort (SIR 0.89; 95% CI 0.77--1.04). When a direct comparison was made between the two cohorts, the eastcoast women displayed an increased breast cancer incidence (incidence rate ratio 1.35, 95% CI 0.98--1.86). No obvious difference was seen between the two cohorts concerning cardiovascular mortality.

Conclusion The results support, but do not prove, the hypothesis of an association between exposure to a mixture of persistent organochlorine compounds through fish consumption and an increased risk for breast cancer.

Key terms breast cancer; cancer incidence; cervical cancer; colon cancer; contamination; dichlorodiphenyltrichloroethane; fish; mortality; multiple myeloma; PCP; persistent organochlorine compound; polychlorinated biphenyl; polychlorinated dibenzo-p-dioxin; polychlorinated dibenzofuran; skin cancer; stomach cancer; woman