Risk of breast cancer in relation to social factors in Denmark.

The influence of social factors on breast cancer risk was examined in a population-based case-control study in Denmark. The case group included 1,486 women, aged less than 70, diagnosed with breast cancer over a one-year period. They were identified from notifications to the nationwide clinical trial of the Danish Breast Cancer Co-operative Group and the Danish Cancer Registry. As controls, an age-stratified sample of 1,336 women was selected from the general population. Data on risk factors were collected by self-administered (mailed) questionnaires. Elevated relative risks (RR) were found for women with husbands in white collar jobs (RR = 1.22), and of the highest social class (RR = 1.35). No clear trend in RR was observed with increasing duration of education. Altogether, the association between breast cancer and high socio-economic status was confirmed, though none of the examined factors was a better predictor of risk than the others. Women working in offices had an increased RR while no other occupation was significantly associated with breast cancer. Social or occupational factors did not explain the urban/rural difference in risk seen in this study.