Breast cancer after a negative screen: follow-up of women participating in the DOM Screening Programme.

First-round screening results for women participating in the DOM project (a screening programme for early detection of breast cancer) are described for the age groups 40-49 and 50-64 at entry. In the younger age group, a low pick-up rate (1.96 per 1000) in proportion to the expected incidence rate in the absence of screening (1.46 per 1000) was found. For the older age group, these rates were 4.25 and 2.03, respectively, per 1000. Interval cancers occurred (relatively) more frequently in younger women. After 2 years the ratio between interval-cancers and screen-detected tumours was about 1:1 in the younger age group and 1:2.5 in the older age group. These different results can be caused by too low a sensitivity of mammography and/or a higher tumour growth rate at a young age. The sensitivity of the screen at various periods of follow-up, was compared: a rapidly decreasing sensitivity of mammography was seen for women under the age of 50, in contrast to a slower decrease for women over this age. This rapid decrease may be caused by a relatively high tumour growth rate in younger women.