Weak associations between sociodemographic factors and breast cancer: possible effects of early detection.

Differences in incidence and survival of breast cancer have been observed to vary with regard to sociodemographic factors. This might be related to variation in frequency of doctor consultation and in time of diagnosis, since sociodemographic factors appear to influence the individual's attention to cancer symptoms and susceptibility to participate in screening programmes. This study aimed to examine the variation in breast cancer incidence and case fatality in sociodemographic groups in Norway, and to discuss whether any variation can result from temporal variation in detection time. The study included 589 521 women with information on residential history, childbearing pattern, educational level and occupational physical activity. Analyses were conducted using Poisson and Cox regression models. Although all the associations were weak, breast cancer incidence was associated with residence in urban areas, high age at first childbirth and high level of education. The urban women also tended to have better survival compared with the rural women. Childlessness was associated with high incidence and high case fatality. A high educational level was associated with the lowest case fatality. This study may emphasize the importance of discussing potential effects of early cancer detection. This is particularly important in epidemiological studies revealing weak associations between sociodemographic factors and breast cancer. Mortality rates may be less influenced by problems associated with early detection and, thus, analyses of breast cancer-specific mortality could give additional information.