The association between stress and breast cancer has been studied, mostly using case-control designs, but rarely examined prospectively. The purpose of this paper is to describe the role of stress as a predictor of subsequent breast cancer. A representative cohort of 1,462 Swedish women aged 38-60 years were followed for 24 years. Stress experience at a baseline examination in 1968-69 was analysed in relation to incidence of breast cancer with proportional hazards regression. Women reporting experience of stress during the five years preceding the first examination displayed a two-fold rate of breast cancer compared with women reporting no stress (age-adjusted relative risk 2.1; 95% CI [1.2-3.7]). This association was independent of potential confounders including reproductive and lifestyle factors. In conclusion, the significant, positive relationship between stress and breast cancer in this prospective study is based on information that is unbiased with respect to knowledge of disease, and can be regarded as more valid than results drawn from case-control studies.
We examined relations between socioeconomic status and cardiovascular disease, cancer, and diabetes mellitus in a 24-year prospective study of 1,462 Swedish women. Two socioeconomic indicators were used: the husband's occupational category for married women and a composite indicator combining women's educational level with household income for all women. The husband's occupational category was strongly associated with cardiovascular disease and cancer mortality in opposite directions, independent of age and other potential confounders. Women with husbands of lower occupational categories had an increased risk of cardiovascular disease mortality [relative risk (RR) = 1.60; 95% confidence interval (95% CI) = 1.09-2.33] while experiencing lower rates of all-site cancer mortality (RR = 0.69; 95% CI = 0.50-0.96). A similar relation was seen with the composite variable: women with low socioeconomic status had an increased risk of cardiovascular disease (RR = 1.37; 95% CI = 1.01-1.84) but a somewhat lower risk for cancer of all sites (RR = 0.86; 95% CI = 0.66-1.11). Finally, morbidity data (diabetes mellitus, stroke, and breast cancer) yielded results that were consistent with the mortality trends, and breast cancer appeared to account for a major part of the association between total cancer and high socioeconomic status. In summary, higher socioeconomic status was associated with decreased cardiovascular disease mortality and excess cancer mortality, in such a way that only a weak association was seen for all-cause mortality.
A longitudinal study of altogether 1462 women aged 38 to 60 years started in Gothenburg, Sweden in 1968-69. Based on information from the population study and from the Swedish Cancer Registry 35 women had a history of malignant disease when initially examined in 1968-69. During a 12-year follow-up period a total of 79 malignant tumours developed in 73 women. A comparison was made between the 1988 Cancer Registry listing and the observations made in the population study. All but one out of 103 cases (99%) were registered in the Cancer Registry and all but one (99%) in the population study. It may be concluded that the accuracy of the population study registration as well as that of the Cancer Registry at that time were very high. This enables us to draw relatively safe conclusions from our own material when testing for risk factors.
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