Breast cancer incidence and mortality in the Nordic capitals, 1970-1998. Trends related to mammography screening programmes.

The aim of the present study was to relate the time trends in breast cancer incidence and mortality to the introduction of mammography screening in the Nordic capitals. Helsinki offered screening to women aged 50-59 starting in 1986. The other three capitals offered screening to women aged 50-69 starting in 1989 in Stockholm, 1991 in Copenhagen, and 1996 in Oslo. Prevalence peaks in breast cancer incidence depended on the age groups covered by the screening, the length of the implementation of screening, and the extent of background opportunistic screening. No mortality reduction following the introduction of screening was visible after seven to 12 years of screening in any of the three capitals where significant effects of the screening on the breast cancer mortality had already been demonstrated by using other analytical methods for the evaluation. No visible effect on mortality reduction was expected in Oslo due to too short an observation period. The study showed that the population-based breast cancer mortality trend is too crude a measure to detect the effect of screening on breast cancer mortality during the first years after the start of a programme.