The underlying annual increase in breast cancer rates in Norway and Sweden before the screening programmes started was 1% or less. For example, the incidence increase in the age group 0-49 years was 0.8% in the period 1990-2001 in Norway.

In first screening round many cancers are detected that normally would have been detected later.

In second and later screening rounds, the incidence rate in the age group invited to screening is expected to be higher than before the screening programme started due to a combined effect of earlier diagnosis and that the breast cancer incidence is increasing with age.